info needed on retro, adjustable rear

Do any of you old farts (of which Iam one) have a Micro rear on your 1911?  If so, is there a model number anywhere on it?  If so, it looks from what I see in an old Shooter's Bible, like it would be one of twelve different possible designations; a number always followed by the letter "P."  Most popular looks to be 1P and 3P which are intended for the 45 ACP in "standard" configuration and "low profile" for the other.  The 2P is listed as being correct for the 1911 in 9mm and 38 Super, and Commander.
I don't know what the difference could possibly be, for example, between the models intended for the Colt 1911 in 45 ACP and the same model in 38 Super, but they are different.  So I would like to positively confirm the model number if anyone here is still using one.
Thanks,
Ed