Given the changes in fixturing and that these were considered experimental, I would rather say they were assembled off line. You don't fix problems with new tools/procedures on the current production line. I agree these were batch built as there was not a production line as we think of it today. I look at the variations as attempts to solve problems identified during the intial work ups. The whole purpose of the batch of 1000 was to get some test beds for troop evaluation, assy plant educations and they were used for later evaluations--takedown butts and grenade launching.