Multiple year serial number. If it's a middleweight frame it's a 57 model.
(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
(1953)
09/01 to 09/03 ------- A47258 ------------------ A62954
09/05 to 09/08 ------- A62955 ------------------ A71782
09/10 to 09/18 ------- A71783 ------------------ A94366
09/18 to 09/21 ------- A94367 ------------------ A99999
09/22 to 09/24 ------- B00001 ------------------ B09436
09/25 to 09/26 ------- B09437 ------------------ B17900
09/26 ------------------ B17901 ------------------ B20750
09/28 to 09/30 ------- B20751 ------------------ B31400
(1957)
Date --------------- Serial #`s From ------------------ To
01/14 ------------------ B18549 ------------------- B22094
01/15 ------------------ B22095 ------------------- B26855
01/16 ------------------ B26856 ------------------- B29069
01/17 ------------------ B29070 ------------------- B31409
01/18 ------------------ B31410 ------------------- B56170