6.5x54R Dutch "37A AI"

I think AI=Artillerie Inrichtingen and 37=1937. What is “A”?
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A = lot designation for case production (?), 1937.

Yes, Lot designation, can go up to B,C and D. ( quarters of the Year???)

Doc AV

In some years in the 1920s the letter suffixes can go up to at least H. Jack