I don't believe it has been suggested that century old guns, in their original condition in terms of their barrels, having to undergo a reproof.
No only those which have been altered. The big problem here is we have not been under the same or similar systems as have the proof countries. These century old guns are not marked as to their original chamber lengths or bore sizes.
Who thus is going to determine if a 12ga for instance having a 2 7/8" chamber & a .752" bore was originally made with that length of chamber & bored for brass shells or if it has been lengthened & honed. On an English gun if it has a .752 bore & a "12" for bore size we know it was altered, not so on a US made gun.
Thus any gun which differes from the "SO-Called Standard" would need proofed or nothing would be accomplished. If I went to sell my 16ga Lefever with 3" chambers is my word that I "Think" it is probably factory good enough. Well if it is you may as well throw it all out the window. Its not the standard 2 9/16" of the era, thus would need proofed. I would personally hate to see it stand proof & then fall in the hands of someone who would begin feeding it a steady diet of the 2 3/4" magnum 16ga loads carrying 1Ľ oz shot, based on the fact it had been proofed. This 16ga Lefever has heavy twist steel 28" bbls having a total weight of 6 3/4 lbs. There is little doubt in my mind it would stand proof, but I don't feed it heavy loads. 1oz is plenty with velocities not over 1200fps or pressures over 8.5K psi. Made somewhere between 1907 & 1915, lock up tight, is not pitted, has a good bit of CC & bbl bluing, why punish it.
I don't need it proofed for my protection, its been proofed by about 100 years of service. As I have stated to give it credability of a modern high pressure smokeless powder proof would actually do more to encourage its abuse than to protect any future owner, but that's just my opinion, but I'm sticking with it till I see some reasonably thought out facts to contrdict.
SAAMI has been recommended as the sourse for proofing. Are they going to set up a secondary proof for older guns on the order of the CIP proofs, I really doubt this could be pulled off. Even if it could I doubt that would have much effect on the folks that it has been stated need protection. They would see the marks, say this gun has been proofed & head for X-Mart for the hottest shells that would fit it.
