I came across this on ebay.http://cgi.ebay.co.uk/FRANK-ZAPPA-MOI-A ... 483fe0d8f7
The bit that got me rooting out my Mono copy was:-
MOTHERS/STAMPERS: 1/R and 1/G (one of the first 300-600 off the press)
I looked at mine and at first I couldn't see anything other than the normal catalogue matrix. But closer inspection I could see a '1' at one side and what at first looks like a U, but actually looks more like I.I at the other. (These are at 3 O' Clock and 9 O' Clock if you have the cat matrix at 6 O' Clock). On the other side (at 9 O' Clock) there is either an A or ^ - or possibly a V if you have the label upside down.
While I was at it, I dug Ruben and the Jets out (also Mono) and on one side there is a 2 and I.I whilst on the other at 9 O' Clock there is GD
I've had these records 20+ years and I've never noticed these extra stampers. Even looking for them I had to hold the records under a light. Any idea what they mean??
Both these LP's are UK issues