I realise that it's not quite like-for-like but there was a later batch of these cases made by Cooke and Perkins (marked C&P) where the left side/front bracket locator was wrongly/insufficiently machined and wouldn't allow the bracket to sit down fully. That meant that the lid wouldn't close down. Easily modified in service by sending down a centralised shell mill cutter.
It looks to me as though these fake/repro tins (let's not mince words here chaps.....) have had the brass insert cast 'to size' and the brass has shrunk while cooling. Incidentally, the nationalk code in that spurious part number indicates Belgium(or is it Germany
). Anyway, whatever it is, it doesn't relate to anything to do with small arms!!!!!