Expert collectors with a lot of experience and some access to factory records can usually determine the DOM od a Model 39 by it's serial number and features.
Everyday working slobs, like me, can determine the DOM of a Model 39a (they're different models, you know) by the SN 's prefix letter, or (if it has no letter prefix) the first two SN digits.
IIRC, the Model 39a's with letter prefixed SN's started in 1946 with a "C". Some letters, like "I" (eye) and "O" (oh) weren't used for obvious reasons.
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