Addendum to what I said about MSB = 17 SIMMS (P2500, PROM, etc.):
Earlier this year I picked up an MSB = 15 SIMM. It shows ups as "MP-7" in my P2500, OS 2.0. Proteum's lookup array yields "MK-6."
The Protozoa SIMM (MSB = 5) shows up as "P/123" in 1 ru boxes.
Years ago I tried making a table of ROM/SIMM resources (number of ROM Instruments, Arps, Riffs, BTS Riffs, etc. with columns for both the common make and the name as it appears in the display. I added what I had and what others posted about when I ran across the info.
Since then, I have compiled tables that list some of the resources (as published, and corrected, if I had info to make the corrections).
From the several comparisons I have made, I believe (without looking it up) with each new version of SIMMs with the same ROM IDs/MSBs (as well as with different ones) additional riffs were added. I'm not 100% sure about this as I don't have every version of every ROM (not even close!) But if I am correct, the last riff (or maybe the number of riffs) might be useful as a ROM NAME Identifier, if it cannot be pulled another way.
OK--the clear, sunny out-of-doors is calling me to come outside and do some more yard work!!!
:-)