On closer look, there is a very, very faint "FR" mark on the right side of the buttstock
FR likely being field or factor repair? It would make sense given a few LB marked small parts.
I initially thought the 9/42 marking would be date of manufacture. Wonder if like you mentioned it could be an FR date?
Your rifle is serial numbered L23843. It is the 3,843 rifle in the L letter batch.
Calculate your rifles manufacture date by month by using the below info -
The first number in the serial number denotes the factory code. 2 is for Fazakerley production
- ROF (Maltby): Identified by serial numbers often starting with a 1 (e.g., 1###x), sometimes stamped with a stylized 'M'.
- ROF (Fazakerley): Identified by serial numbers often starting with a 2 (e.g., 2###x). Post-war rifles often used PF or PF2 prefixes.
- BSA Shirley (M47C): Identified by serial numbers often starting with a 3 (e.g., 3###x). Early production (1941–1943) used 4-digit numbers, while later (1944) used 5 digits, often marked M47C.
- Maltby proofed its first 25 rifles in June of 1941, Fazakerley its first 300 rifles in July of 1941 and BSA Shirley its first lot of 300 rifles in August of 1941.
No. 4 Mk I Fazakerley production serials were assigned as follows:
20000 thru 29999 for the first 10,000 starting in July of 1941
A20000 thru A29999 for the second 10,000 starting in August of 1941
B20000 thru B29999 and so on thru the Z prefix series.
That's 10,000 rifles per block x 26 blocks = 260,000 rifles plus the first unlettered serial number range = 270,000 rifles to SN Z29999
Then two letter prefixes starting at AA thru AZ
Considering A thru Z represents 260,000 rifles then with repeating this to LZ (latest dated serial number seen) would be way more than were actually produced (10,000 per single letter block x 26 single letter blocks x 12 double letter blocks to LZ > 3 Million rifles).
Production Volume: During the peak war years, Fazakerley produced, on average, approximately
10,000 to a max of 12,000+ rifles per month, often marked by serial number prefix changes (e.g., A, B, C prefixes, etc.) representing roughly 10,000 rifles per block.
Wartime production volume started to drop off after late 1943.
Post war Faz serial numbers were in the PF2###X serial range.
Total Wartime Production: ROF Fazakerley produced a total of 619,913 No.4 Mk1 rifles during the war (1941–1945).