I can’t fathom how many suppliers GM (and/or AC Delco) must have had over the decades…nor the huge staff that must surely be required to keep track of it all.
It’s certainly plausible that reorganization of brands and marketing divisions resulted in some supplier changes along the way.
For example, the ignition module in question is sold via AC Delco distribution networks and via GM dealerships. Same part. The packaging carries the AC Delco part number and the regular GM part number.
The dealership could buy the part from GMSPO or they could buy it from AC Delco…two different business entities but both part of General Motors
The “AC” comes from “Albert Champion”…of spark plug fame.
“Delco” comes from “Dayton Enginering Laboratories Company”, according to Wikipedia