It could have been donated/taken in to service in an emergency (WW1, Post Dunkirk etc.) or perhaps it was a commercial sale to foreign military who follow Britishicon practices.

I suppose it could also have been a private purchase by a wealthy commanding officer. I can’t think of an example off the top of my head but I mean something along the lines of a Lord setting up his own battalion and buying equipment privately. I’m sure I read this happened at the start of WW1.