For me, choosing between the 7mm short mags. or a .280 IMP would boil down to brass availability. There is a ton of '06 brass and '06 based brass out there that is all useable - all the way up to .35 Whelen brass. For me, brass availability makes it a "no question" as to why would I choose the .280IMP.

As far as head stamps, I've necked down and rim trimmed brass marked .45/70 for a 2" .375 calibre Mauser barrel and the same rifle uses brass that has a .350 Rem Mag. stamp on it. Also, in my stuff are boxes of ammo with IVI69, LC73, .308, 7mm/08, .260 Rem. and .243 stamped brass that is necked to .260 or .358 in loaded and 'empty' brass cans for a .260 or .356 Winchester. With them, there no problem seeing what's what. Even the 9.3x57, .9.3x62 & .375'06/IMP is easily separated - ctg. length, bullets loaded and shoulder shape easily distinguish them. These are only a couple examples - head stamps are not important to me. Merely looking at the case or loaded round imakes it easy to identify it & thus the rifle it fits.
With a 9.3x57IMP and a 9.5x57IMP, or a 9x57 and 9.3x57, one might want some other method than visual for distinguishing them, like a proper headstamp - or a confined bullet choice would work.
Now, if the calibres were closer together, with identical shoulders, the proper headstamp might be important.