Newbie question on NZ Long Branch

[52m37]

Hello All
New to this forum.
I have a 1942 Long Branch, No4 Mk1*.
It has the LB serial number and above another serial number.
Please tell me what the second serial number is. Is it the NZ number?

I have a lot of reading left to do so if this is an obvios question or have been discussed before, sorry. There is just so much information on this forum that I have not digested yet.
Thanks

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