system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 The USSR under Stalin was exposed to a lot of propaganda and facts were conveniently altered, so how did historians decide what was likely the truth about that time period?
gpt
This is actually a true problem. As offical statistics are often problematic, historians have to take into account various other sources,  e.g. private notes, media coverage from contemporaries, crossreferencing the "offical " event with internal reports or other non-secret notes,  secret service infos (if available) and several other sources.

In the end it is often just enough for a rough estimate. We'll likley never know how many people died during the great jump forward in china, or other things. Just a rough estimation which may very well be off,  but is the best we can currently reconstruct with the available data.