They were made since 1947, numbered with all other A-5's, but after 1953, there are no Belgium LIGHT 12 shotguns with a non-prefixed serial number.
After that, they all had a letter prefix of either "L" (1953-1956) or "G" (1957 & part of 1958) or (after sometime in 1958) a short number denoting the year followed by a "G" and the rest of the serial number (69Gxxxx = 1969).
If "L860" is the serial number, it's a 1953 run for that model - and the barrel length should be 26".
A serial number in the 44,000 range, as you said it has, would put it as 1913 - much too early for that model.
However, if you typo'd the serial number, and it's in the 400,000 range - it would be about 1954.
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