World War II seems like an easy one. A well-read historian in 1969 would be missing a lot of important history that has come to light in the past 50 years.

As u/Georgy_K_Zhukov pointed out in this previous answer, the availability of new information to Western historians about the Eastern Front has changed drastically, and has pretty radically altered conceptions of how that particular war was fought, and its relative significance to the greater global conflict. English-language histories of the Eastern Front in the 1960s still relied heavily on information from former German officers, and these accounts were both self-serving, played up the "clean Wehrmacht" myth, and played down the effectiveness of the Soviet military in dismissive and often racist terminology.

A historian in 1969 would also be unaware of Ultra and it's role in cracking the Enigma cypher, as this was not declassified until the 1970s. When this information came to light it also pretty radically altered histories of the war.

Understanding of the Holocaust was developing in the 1960s, and had only really begun to be discussed with Eichmann's trial (Eichmann himself has been pretty seriously re-evaluated since Hannah Arendt, by the way). It like the Eastern Front has benefitted from the opening of archival material in Eastern Europe and the former Soviet Union.

Speaking of the USSR, it's historiography has changed radically since the 1960s, in part because that was when the revisionist school began to challenge the totalitarian school. The totalitarian school maintained that a small group of leaders in the USSR maintained absolute control over every aspect of life in the country, in a system that was similar to Nazi Germany - neither Soviet nor German historians would seriously subscribe to any of this any more. Soviet historiography has also changed in that it has an endpoint now, which necessarily influences how historians go back and approach earlier events. For example, the world-historical importance of the October 1917 revolution has tended to be re-evaluated, and much more study and interest given to the February Revolution and World War I in Russia. Indeed, national histories in the former USSR have been given much more study as they are histories of now-independent countries. It would have been common in 1969 for a well-educated American historian to associate "Soviet" with simply "Russian".

Finally, it all depends what one means by "basics". Areas like social history, gender history, economic history, cultural history, and heck, even sports history really have developed since the 1960s, and these are pretty fundamental to our understanding of the past.