in the episode "SMILIN' JACK" Col. Potter's telling Hawkeye and B.J. in one scene about a chopper pilot he knew in WW I. But helicopters weren't around then.

I'll put this inconsistency here: in season 3, episode 7 Trapper is diagnosed with an ulcer and nearly sent home. Just two episodes later he's drinking like a fish in the "Alcoholics Unanimous," episode without any indication that he's supposed to be watching his diet.
well, that one could be explained by the fact that TV shows aren't always shown in the order they're filmed in. The 3rd episode filmed might be the 7th one shown for example. So maybe "ALCOHOLICS UNANIMOUS" was filmed before the ulcer one and they originally planned to show them in that order but something happened to prevent that.

In the last season the last episode they filmed was "AS TIME GOES BY" even though the finale was the last one broadcast.

What about every time Radar or Klinger had a date with a nurse? As you may know, enlisted personnel are strictly prohibited from dating officers.