To those military experts A.M 6B/159

Looking for a little information please
I’ve been trying find an 6B/159 for a while and most are over £1000 so I definitely want a little information before I pull the plug

I’m looking at one which needs a little work
The movement number dates to 1943 and is 9738***
Engraving to the back cover is A.M 6B/159 6459/43
So if genuine the case does match up to the movement and to the date issued for a 6B/159
The question I have it’s got an 8 digit case number of 10541704 instead of the normal 4 digit like a 2292 ect
Would this have been a replacement back cover and re engraved or is this a genuine case I just haven’t seen many with the 8 digit number inside
Any help would be much appreciate

No this is completely normal for some of them. I wouldn't be concerned with that at all. But of course pictures speak 1000 words.