You could well be correct in your dating of the finish of blued action on lp53s.My extensive collection of said model extends to some 28 approx,i will have to count them to be certain of numbers.My first blued version is serial No. 003137 which is the first year of production 1953.The last blued version i own is a 1956 de-lux boxed version adjustable trigger serial No.17747.A 1957 de-lux boxed version with fitted barrel weight
adj. trigger. Serial number 21090.Has the fine crackle finish, so has serial number 21010 1957.So abit before the 24000 mark.
Roly.