Originally Posted by CV-6

I was going to query you on that as I had not seen any info supporting the contractor letter. But I did one more search and came across a Brian Bayliss post on CR that said just that.

Part of his post below...

Serial numbers on Italian built Masis are a little more difficult to
know everything about, but still much is known. At that time Masi frames
were built my several sub-contractors in various cities near Milano. I
have seen one Italian Masi with only a size stamped on it and no letter
preceeding it which indicated the contractor. I have seen one frame with
the letters of two different contractors preceeding the size. Since
there were all these independant builders I don't think it all that
unusual that there are some inconsistant markings from time to time. So
far I have seen these letters used: M, A, B, P, V, AV, and one that is
an "M" but it's upside down (which is easy to to when using number
stamps). If anyone else has a pre 1973 Italian Masi that has any other
letter or combination, please let me know so I can take note of it.

Learn something every day. Too bad we do not know who the contractors were for each letter.