I find the census number very interesting, I am assuming the '20' under the NZmarking is the *Census number.
I've never seen a two digit number, so I wonder if the batch of 4T's provided was sequentially numbered?
* NZ individually numbered all service firearms, from the P53,(or perhaps Snider) through to the L1A1 and the Sterling.
Finally discontinuing the numbering system in 1959.