The answer unfortunately is "it depends."

The Cold War created problems for scholars on both sides of the Iron Curtain. Obviously, there were clear limits on archival access, or even access to the country at all, on the Soviet side of things. The source bases for areas such as high political policy, the police state, national security, and foreign policy were incredibly thin during the Cold War. The main archives available to Western scholars were the Central State Archive of the October Revolution (TsGAOR) and the Central State Archive of the National Economy (TsGANKh). Foreign scholars had their own separate reading rooms, had no access to inventories or catalogues (opisi), and were thus at the mercy of the archivists. TsGAOR and TsGANKh archives also forbid access to sensitive areas such the rationale behind economic decisions. This constrained view is one of reasons why Cold War-era books on these subjects tend to have a degree of conjecture within them. Scholars also had to tread a very fine line within the USSR and ensure they did not set off any ideological alarms. Sheila Fitzpatrick recalled in her memoir A Spy in the Archives that one Soviet publication denounced an article by "S. Fitzpatrick" and she was lucky that the Soviet author blithely assumed she was a male scholar, otherwise she might not have been able to continue her research inside the USSR.

But the problems for scholars did not only originate from the political imperatives of Moscow. The US academy in particular was dominated for about two generations by 1917 emigres and their kin/students who generally held a very dim view of the Soviet experiment. The so-called Menshevik interpretation of the Russian Revolution- that tsarist Russia was too autocratic to have a genuine revolution and Lenin's dictatorship was a natural consequence of this maldevelopment- was one of the basic orthodoxies among this set. The Cold War also lavished a degree of funding on the Russianists who filtered into various Kremlinologist think tanks. Some of the work that resulted from this political situation, most notably that of Richard Pipes, was characterized by a bipolar reading of the USSR in which it was simultaneously a totalitarian juggernaut and a crude inefficient state. In the case of military affairs, there were a number of defectors like Viktor Suvorov who cast a baleful influence on this field. These men would often cite themselves as an authority on Soviet military affairs and would use their past credentials to buttress their alarmist tales. These defectors often found that they had a ready audience for tales of the imminent Soviet threat and its cheating on arms control treaties. Suvorov, for example, produced a number of works arguing that the Soviet military equipment the West had encountered in proxy wars were so-called "monkey models" downgraded for export and that the Soviets' actual equipment was more capable. While it was true that some Soviet exports of military equipment were downgraded models, which was par for the course for most arms exporters during the Cold War, Suvorov's contention took on a sinister gloss when combined with his assertion that the USSR had an expansionist drive that dated back to Stalin and the complete subordination of the military to the Communist Party. While there were a few responsible scholars on Soviet military affairs during the Cold War such as John Erickson, the more questionable writers outnumbered them.

The Cold War does not mean that all pre-1991 books should be ignored though. While certain topics were forbidden or difficult to research, there were cracks in the system. The events of 1917 and the 1920s period were relatively open for Western scholars to write about. The emigres had brought over a number of archives on this period and the Soviets did preserve a number of archival holdings that were comparatively easy to access like Central State Archive of Literature and Art (TsGAL). The new social history of the 1960s was also something that the ideological gatekeepers on both sides of the Iron Curtain were able to handle. One of the curious facets of the revisionist interpretation of 1917 was that historians like Alexander Rabinowitch and Fitzpatrick were attacked both in the Soviet press as capitalist stooges and by the Kremlinologists in the Western press as Soviet dupes. Glasnost and Perestroika accelerated the penetration of social historians within the USSR as the state was more amenable to allowing Western scholars access for the human face of the USSR's history. The Gorbachev period saw an increased access to regional oblast archives and Western scholars branching out to areas beyond Leningrad and Moscow. Both Stephen Wheatcroft and Robert W. Davies were able to use the increased access to TsGANKh archives to produce some pathbreaking work on the Soviet economy. The 1980s also witnessed the start of Soviet labor history which did not easily fit into neat Cold War paradigms of a cowed Soviet working class or a proletariat uplifted by the Soviet state.

But there were limits even in the most open days of the Gorbachev period. Studies into the Stalin Terror and the Gulag remained fairly off-limits until the collapse of the USSR. Likewise, a systematic and fair history of the Soviet military was only really tackled in the West after the fall of the USSR by historians like David Glantz. The collapse of the Soviet state also meant that foreign scholars finally had access to the opisi for the relevant archives and there was a great deal more access to local archives than ever before. Stephen Kotkin's monumental Magnetic Mountain was just one example of how access to local archives could transform the field as Kotkin used the Stalinist mega-project of Magnitogorsk in the Urals to uncover a wider picture of society under Stalin.

One of Kotkin's favorite quips is that that the opening of the archives revealed there were no secrets. Kotkin and a number of other Soviet scholars have discovered that the ideological rhetoric the Soviet leadership projected outside was mirrored in their own internal conversations. This ran counter to some of the Kremlinologists' picture of a cynical Soviet leaderships' will to power. While Kotkin's aphorism can go too far, it is important to realize that the 1991 archival caesura was not always that transformational. Cold War-era practices of limiting access to archives and their opisi are still in place for some sensitive areas such as foreign policy and the FSB has curtailed access into the archives of the security police in their various incarnations. One aspect of the Cold War researchers' life that has a renewed salience in the Putin era is the importance of personal contacts. Scholars like Wheatcroft and Fitzpatrick were able to use the Detente period to build personal connections that allowed them access to resources and other hard to reach information. And while personal connections have always helped historical researchers, it has renewed importance in the Putin era where there are greater hurdles to working in Russia. The popular historian Simon Sebag Montefiore alleges that he received access to a number of documents on Stalin because his earlier book on Prince Potemkin caught the eye of one of Putin's advisors. Chris Miller's recent book on the Gorbachev period, The Struggle to Save the Soviet Economy, has some fascinating details because he had access to the Gorbachev Foundation Archives which has documentation from Gorbachev's Politburo.

So for pre-1991 works, I would suggest the following criteria:

• Who is the author? Really delve into the author's CV and biography. Some authors will leave a paper trail to other aspects of studying the USSR while it existed. Connections to Cold Warriors like Robert Conquest or think tanks like Team B are automatic red flags in terms of bias and reliability.

• What is the source base? As the above shows, research into the USSR was not easy. A glance at a bibliography or citations should show something of the methodology that underpinned the book. Research within the USSR is obviously a plus, but not an automatic qualification.

• Who is the audience for the book? There was a market in Soviet studies for certain types of books, especially the alarmist ones. /u/lazespud2 has a fascinating answer of theirs on left-wing terrorism and a feedback loop between authors and policymakers. The post-1991 archival situation has shown the realities were often much more messy and less sinister in a number of areas. Nuclear issues is one field in which there were a number of hyperbolic books produced for people who wanted their worst fears confirmed about the USSR.Steven Zaloga noted in The Kremlin's Nuclear Sword, the lack of information on the Soviet nuclear program led a number of writers to project an idealized narrative in which strategy, development, procurement, and deployment proceeded in a harmonious fashion when the reality was quite different.

• Are there outdated paradigms? This necessitates a certain familiarity with the wider historiography and the theory of history. There were a number of frameworks popular during the Cold War, most notably the totalitarian thesis, that are quite passé in 2018. A good deal of the work produced on the Eastern bloc states during the Cold War is just not that useful today because the authors often took it as a given that the Communist leaders were puppets of Moscow. The archives of the Warsaw Pact countries, which are much more open than those of the Russian federation, show a much more complicated picture of subordination and independence.