Collectors will know more but I just had a look at Knibb's What's My BSA and all the prefixes you speak of are there. I did not know that the 1st Airsporter was called the club. then the Airsporter club 1948-50 and 1950-54 respectively.
Of course this does not help with parts but What's My BSA will give you a start.
E for .177 and G for.22. Just off to double check my 22 now.