Try head badge dating-
http://www.velobase.com/ListHeadBadges.aspx?Offset=7&GroupBy=brand
I think that bsa had a serial # dating for there hubs as well but not positive
BSA DATING by Steve Griffith
Frame numbers are a notoriously poor guide to BSA dating. They were not sequential and there are no
known company records. However, in the VCC BSA file are the ledgers from Astleys of Oldham (1934
to 70) who were a large volume seller (50 to 120 bikes a year). These provide a useful part of the
jigsaw but it is important to remember we are a long way from having a complete chronological frame
record. The information from Astley ledgers can be summarised as follows:
-Tandems from 1935 to 1940 begin with AD, AE, AT followed by a four or five digit number.
-For 1934 majority of numbers begin with the letter W then a 5-digit letter begins with a 3 or 4.
-For the period 1935 to 39 the letter is WE or WD or H with a 5 or 6-digit number
-For the period 1942 to 1950 there is no letter just a 5 or 6 digit number.
-Beginning in 1951 a letter prefix was re-introduced running A to E.
-Post 1959 the letter becomes a suffix usually 2 letters.
There is no correlation between models and frame number e.g. sequential number may be roadsters or
lightweights
Hope this helps