Beats me. My oldest 1941 No4MkI is 0L244. Can't remember the numbers on the other 1941 or my 1942 No4MkI or No4MkI*.
As far as I understand the rationale, the 'L' was just a location identifier for Long Branch, the same way the American Savage No4 rifles made at their Chicopee Falls site have a 'C' in their numbers.
The letter isn't part of the serial numbering sequence at all, meaning 0L25 is the 25th rifle made, 0L9999 is the 9,999th, and 1L0001 is the 10,001st. (Have to dig out Stratton's books to be sure.)
The sequences ran continuous from beginning to end, without changing the number range as a new year began. The barrels & receivers were dated with the year each were made, though there is always the possibility of mixed barrel & receiver dates for rifles assembled around the new year. Of course there's always the possibility of later barrel replacements in service or otherwise. I have even heard situations where for whatever reason all other parts were saved but a receiver was scrapped: the receiver was replaced with a factory 'spare', which as manufactured was marked WITH the year it was produced, but WITHOUT a serial number. After replacement it would then be serialised to the rifle that the scrapped reciever came from. I once saw an example like this at a gunshow: a very early serial number Long Branch. All numbers matched, and the number should have put it in early 1942 as a No4MkI. The receiver was a later-dated No4MkI* ? Only some government accountant could make sense of the idea of a receiver being replaced but the rifle staying the same.
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