52 numbers have a letter and 6 digits....mid 48 they start having 6 digits after the letter. Before that it's letter plus 5... this applies to bb stampings... so up to 52... 53 it's stamped on the dropout... and starts over again ish
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Aaaaah, but wait. The 1952 numbers have a letter and 5 digits. 1952 was also when the SN's started being stamped on the rear dropout. 1953 also has a letter and 5 digits so this is how I figured out the bike is a 47 model from what info the OP first posted. By the way, the SN with the letter and 6 digits started in April 58 when the numbers were stamped on the dropout.
(1952) Date ------------- Serial #`s From ----------------- To
01/01 to 01/07 ------- A87594 ------------------ A92478
01/08 ------------------ A92479 ------------------ A97866
01/09 ------------------ A97867 ------------------ E00434
01/10 to 01/14 ------- B00435 ------------------ E05720
02/06 to 01/07 ------- B05721 ------------------ E12209
02/12 to 02/19 ------- B12210 ------------------ B33998
03/04 to 03/31 ------- B33999 ------------------ B78697
04/04 to 04/30 ------- B78698 ------------------ E99356
05/01 ------------------ B99357 ------------------ B99999
And here is the 1947 info?
1947 SN's BXXXXX CXXXXX with possibly a few higher AXXXXX numbers