One of my MMs has kind of strange serial - “P-149”. They normally are a 4 digit number (like “1234”). Is this perhaps a prototype or one given to a special client?
“one of my MMs…” ? How many do you have ? 
Would you accept an arm and a leg for one of them ? 
I have 2 as well…both have a 4 digit serial #. Even the LAMM from Rudi has the original serial #. Maybe yours is a prototype?
I remember going to the Moog factory in Buffalo back in 1983; They had a 4 tier A-frame stand stocked with 4 MM’s in a demo room; maybe it’s one of those?
Cheers
Check the front panel boards. My MM has the serial # hand written there with permanent marker.
Also check the datecodes on the ICs, they give the best indication of when it was made. Memorymoog was released in 1982.