Interesting point. I suppose that would be good for some wishing comformity.

I've been shooting non-correct headstamp cases for so many years, I don't even think of them any more. My first wildcat, a .257 Ackley Improved, had 6mm Rem, 7x57 Mauser and 8x47 Mauser headstamped cases for the three different bullet weights I used, one for each. My .458 2" had .264 WinMag to .458 Win mag and every make and headstamp in between - 7mm Mag, .300 Win Mag, .308 Norma Mag., .300 wTBY Mag., .350 Rem Mag. and .338 Win Mag and all different mades as well. I found the .458 did not care what make they were - still plunked them into tiny groups.
For the .416, I'd probably stick with .338
Win. Mag or .458 Win. mag. - or both - each for different bullet weights.