Mamiya 7 Lens Serial Numbers

[bwcolor]

I'm trying to sort out the age of some of my lenses. For example, I have two 80mm lenses with differing letters associated with the SN. Does anyone have a good URL for sorting out this sort of thing?

 

[qruyk12]

from 2001 on it was easy. A = 2001 B=2002 etc... older lenses as i recall started with O,P,Q etc...