Here are some pictures to support the discriptions and the discussion. Will let Bon expand or explain more if he chooses.
Pic #1 Base without the nipple/breather tube but with the cast provision
Pic #2 Base with the nipple/breather tube attachment
Pic #3 Side by side
Pic #4 Interior/top side of the base
Given all the early/late and the variations it can get confusing and that's just the base