To be fair, there is also a distinct line between 'retool/pretool' and 'shared engineering'. If a transformation works, there's no rule that says two distinct molds can't have the same transformation design. We've just gotten so used to the practice of pre-planned shared molds that the automatic reaction when a figure is revealed is "Who is this retooled from?/Who can it be retooled into?".
It is fun to see bits of shared engineering or just "shared ways of doing __________," even years later, like seeing something that works the way the Alternators did way down the line.