I’m not sure it’s documented anywhere, but if you read anything by Trotsky on there it’s full of inline notes to explain what he means, and these notes are full of words like “Stalinists” or “bureaucrats” lol.

Here they admit themselves to editing Lenin to remove “pro-Stalin bias” from editors: https://www.marxists.org/archive/lenin/works/note.htm

They also removed portions from Mastering Bolshevism about restraint and care, compare yourself:

https://www.marxists.org/reference/archive/stalin/works/1937/03/03.htm

http://www.marx2mao.com/Stalin/MB37.html