SID Chip Markings and Revisions

top markings bottom markings
MOS 6581 2282 AM211713 KOREA (filter is blown)
MOS 6581 2383 AH225704 KOREA (dead)
MOS 6581 2383 AH225705 KOREA (dead)
MOS 6581 1284 DH015117 PHILIPPINES
MOS 6581 1884 TH136576 THAILAND
MOS 6581 2184 AH153572 KOREA
MOS 6581 2284 NM192192 TAIWAN (this one of the ebay remarked chips)
MOS 6581 4684 AH127608 2 KOREA
MOS 6581 CBM 2285 AH111555 3 KOREA
MOS 6581R4AR 3586 S HH332126 HC-30 HONG KONG
MOS 6581R4AR 4086 14 HH392108 HC-30 HONG KONG
MOS 6581R4AR 4986 14 HH462130 HC-30 HONG KONG

MOS 6582 3186 25 HM292833 HC-30 HONG KONG
MOS 8580R5 0987 25 HH076904 HC-30 HONG KONG

After seeing this stuff, I have some theories about the bottom markings:

The first letter denotes the fab, the second letter I am not too sure about, while the next two numbers are the week the dice were made. the remaining 4 letters are a wafer lot code most likely. Some chips have a number after this which appears to be the die revision, but only from late 84 on appears to have it. The 4684 and 2285 date coded chips have a 2 and 3, respectively which appears to be the die revision.

Later chips were actually marked R3 (at the tail end of production) and all R4 and on chips were marked. The only exception I can find is my 6582 chip which has to be an R5 no matter what.