And that's because the basic design was little changed until the end of the .303 era. The tapered lid apparently designed with so steep a taper that it could be hammered out of position no matter how water-logged or covered in dirt and dust.
The one I have here is marked as to be turned in for re-use, but this collection of the brass keys I acquired somewhere suggests either the boxes were getting burned or some thrifty soul was collecting the keys before the boxes were sent back for reuse. [Upon checking I see this box is not so marked - must have been another I saw previously]
Also have an old box dated 1909 which is quite different and may be a Canadian pattern.