Strange wagon plate

A friend of mine was given this plate.
Can anyone explain the obvious difference to a normal Wagon Plate?

It is a complete mystery as I cannot identify it in either my LNER or BR wagon books.
I’m guessing it must be a four -wheel hopper wagon

No idea if the paint is original or not.
Why the 4 boltholes?

 

No one got any ideas as to why it is made of brass?
I do not think it is a fake or replica, knowing the ownership for the last 30 years or more.

 

The quality of the cast looks exceedingly poor, almost as if someone has used an existing wagon plate as a pattern to make a brass one. For what reason, I can't suggest.

 

https://www.easyliveauction.com/cat...9357e7ef448a6646f/railwayana-auction-lot-220/


https://www.madmantiques.co.uk/webs...on-wagon-d-plate-standard-21-tons-1947-steam/



The vast majority online seem to be like that, with L.N.E.R. However, I've found these...

https://www.gwra.co.uk/auctions/lner-d-wagonplate-together-track-circuit-plate-lne-2019apr-0545.html



https://www.lot-art.com/auction-lot...092-anot/1289-variou_railway-22.7.21-fielding




which match with L N E R and the deformed 3 at the start of the number. Numbers indicate the same batch as well.

Definitely a 21T hopper.

https://paulbartlett.zenfolio.com/lnerhopper21ton/h35e87b32

As to why it's brass, no idea! Plated by someone? The two round holes aren't original, and they're not level either.

 

Prob. Repro. but as already asked, why?
Or..... was there an exhibition around that time that included a 21T hopper wagon.
The railways did like to bull up exhibited items and that might include worksplates etc.
Just a thought.