I really doubt when the car was built it had one side is different from the other BUT who's to say sometimes ?. Maybe with some close looking you might be able to see evidence of if something was changed at some point in the cars life.
I will say, I have welded on hinges on my 73's and 74's and like them but I know if I had the adjustability of bolt on ones, I would maybe go with that type.
I know years ago I bought some internal paperwork that was originally from GM corporate headquarters and documented meetings they had on Thursdays and it was interesting in that they said that on a certain week, they would be out of motors or transmissions, or whatever due to some unforseen issue and would not produce a vehicle a certain way during a particular time frame. They were getting some parts from different suppliers and not everything came in on time or they had unexpected runs on something.
Pretty sure the welded hinges started in '71, my '72 is welded. The hinge probably broke and a bolt on was retro fitted. If you care to go deeper into it you can remove the kick panels and look at the backside of the door hinge if there is no obvious clues from the outside.