See, this is how the myth that Soviet soldiers had to share the same rifle spread, Nazis were basically gun loot boxes so everyone was changing loadouts.
Yes very likely, the round air-cooling holes are a good hint, although they can also be found on the MG30 but those didn't use drum magazines, the MG15 did but it had square air-cooling holes.
Also I think the other models didn't have the buttstock removable while still operational. That's because the MG34 later was often used as a vehicle mg in tanks and the like, where space was limited.
During my mandatory service we trained with the MG3 (still in service) which is the successor and basically almost a copy of the mg42 and removing the buttstock would remove the recoil spring.