WW2 No.36 Mills Marking Question

[Matthew Lawton]

Hey guys.
I have this No.36 by J P & S and it is marked 49 on the back under the lever.
Any ideas what it refers to? Date?

Photos attached.

Best regards
Matthew

 

[BMG50]

More a cast number than a date, as I have the number 25 on my JP&S in the same place and it certainly wasn't made in 1925.