Never got a good explanation for all the strange prefixes and suffixes after the base part number - but all of these transmissions should have had a PK in front.
I can't confirm a story I heard but some units were shipped in pieces then "built" at another location - but that has never been confirmed.
The suffix after the part number may have something to do with the line that built the unit.
The plant so many transmissions that is is likely to have had more than one line - or shifts - and the alpha may be for tracking line or shift.

Only a few people are alive that still work at the plant - they may know the real reason.