Some of that haphazzard panning happened when (AFAIK, please correct me if this is wrong) the Beatles' 4-track recordings were sent to the US to cut the records for the american market.
The tapes had been recorded with a mono final mix in mind, but accross the pond someone must have thought "we have stereo now, so we'll mix it down to stereo"
That, and probably the fact that panning was only switchable at the time, made for those weird mixes.