The mechanics were not seperated into DL 142. Everyone was DL 141, in order to stave off an AMFA raid the IAM conducted a vote and the mechanic and related at 141 voted to form their own district in 1999, which was four years after the ramp at US became IAM, which was DL 141M., not DL 142. 141 was still the largest Air Transport DL in the IAM.
When UAL mechanics went AMFA, 141Ms resources could not let it survive, then we were merged into DL 142 last year, as it was the only District with mechanics in it, as 141 was purely Fleet Service and Customer Service.
And if there was ever an IAM represented group on strike at US the other group would honor the picket line, being part of or not part of the same DL does not matter.
Don't let the facts get in your way.