RMC would put whatever you wanted on the head-stamp.   handy for recreating oddball cartridges.   So your cases might have been commissioned by someone with the initials G.A.D  a call to RMC might clarify that----if the new owner has the old records available.

I had a odd chamber variant on the 43 BN Mauser in a nice early german stalking rifle/  I had RMC makes some custom cases based on a chamber cast----chamber contour on the outside and a straight bored powder chamber inside--thicks walled--sort of super everlasting case.   when he asked how I wanted the head stamp we stamped the head with the cal. and the gunmaker/or owner's name based on the marking on the gun.