No. Conquest was working from guesstimates, speculation and rumour. We know a lot more about Soviet population movements and repression deaths now than was known when he was making a name for himself. In particular the suppressed 1937 census results became available in the 1990s, refuting a good part of the speculation about the overcount in the 1939 re-run. Demographers (starting with Frank Lorimer 70 years ago) have similarly disproved the regime's inflated claims for natural population growth after the 1926 census, which underpinned much of the alleged excess mortality estimates. That millions died through famine (most of the loss) and repression is certain: that it was anything like 30 million is an article of faith unsupported by evidence. How much of the loss in 1941-45 should be attributed to Stalin seems a matter of ideological taste, depending on how much responsibility one attributes to the fact of invasion by a genocidal enemy.