Okay so all primary sources will be colored with the historical and political context and ideology of the writer. One thing to consider when looking at a primary source is who the audience was. Sources for the public, such as the conspiracy laden Pravda were designed by the party for particular aims of getting the public to believe things, and the writers themselves were brought up in a conspiracy prone institution (after all the party was facing so many threats and wars and secrecy that it ended up just laying on conspiracy theories in it's own documents). Then there are documents that were considered for different levels of the party, and there are conditions of that institutions that result in those documents having their own biases. Generally internal documents that were pulled out of archives are factually accurate in that they are the real beliefs of the people writing them, and figures on material items are not too far off. However the conditions of the institutions and people in the party can result in clashes in conflicting documents. For example figures on grain production internal to the party were actually accurate, however sections of the party, and Stalin, thought they were lying. Furthermore, some of the collectivization drives may have actually been highly influenced by a conspiracy theory that Britain was going to invade via central Asia, which got into the zeitgeist of the party in 1927 (even though in reality the British empire was already beginning to crumble, they were blinded with the pre revolution status of Britain as the biggest imperial threat)

Also really keep in mind that anything published as political theory will be extremely colored by political context, and the actual ideology of the writer.