As I read it, they copied optional screw fitting holes and badly assembled parts because from an abundance of caution they didn't know what was optional or mandatory.

I watch russion tv and they said that they copied personal photo cameras that pilots took with them. They thought that those cameras may be actually supplied with every US bomber in order to make photos of the enemy territory.

That's just cold war propoganda. They had four B-29s that they cross-referenced in the reverse engineering process, so patches and mis production issues that only affected one were left off.

They did go to great lengths to clone though, but that was a "we can do exactly what you can in two years from essentially nothing" international politics dick measuring contest. Anything other than an exact clone would lead to a "look at how the commies can only make an inferior clone" talking point.

Probably has more to do with not wanting to piss off Stalin

Exactly.

Not battle damage, mistakes in production (an extraneous hole drilled in wromg location etc).