IBM codes

[UMMR]

Hello,
I'm searching for more info about the mysterious IBM chip codes like IBM 22, IBM 52, IBM 9314, IBM 7070 and so on. I have in my collection more than 20 different codes and combination of codes!
IMHO they identify the fabrication/assembly plant, but this theory has some inconsistencies.
Apparently they are unrelated to the chip package type (you can find many different packages marked IBM 52), the pin count, the surrounding chip technology and the system in which the chip is installed.
I know the memories marked 7070, 7074 and 74 are manufactured by IBM Esslingen (Germany) or IBM Burlington (US).
But what about the ubiquitous and immortal IBM 52 (seen in a 1971 SLT card as well as in a 2001 POWER4+ CPU board)? And the IBM 9314 (in my experience many IBM 9314 chips are CMOS)...?
What can be the "PQ" code seen in so many different chips?
Why there are around 486DX/2 50 and 66, **with Intel logo**, marked IBM 9314? Maybe they have been manufactured directly by IBM? Here is an example: http://www.ebay.com/itm/Intel-03H4938-486DX2-50-Processor-IBM9314-/200840754831?pt=CPUs&hash=item2ec30ab68f.
Any help will be appreciated!
Best,
Paolo