Gajin usually uses official public sources where possible, assuming that they are correct, and all tanks were made to spec, which is fair for praticality but maybe sometimes the spec was a suggestion, and sometimes the "spec" wasnt so real and was a carefully planted lie

Reports from oposite intelegence agencies are probably more likely to have less lies but at same time are usually top secret and have way less concrete info to work on

And there is also wear and tear, lack of maintaince, unproper storage, maybe the steel just got a bit rusty

... Their bias was a lot more blatent back in the early days, but yeah, you're right.