Correct me if I am wrong here, but my memory seems to tell me the in between gauge marks (IE 9/1, 9/2) were not used prior to 1887. Thus a bore marked 9 could have varied anywhere between just large enough to accept an .803" dia plug gage to 9" to just small enough to Not accept an .835" 8 ga plug to the same point. It would have been out of proof upon accepting the next plug up the ladder. If we attempt to apply this retro many guns went "Out of Proof" in 1887. An 1884 gun with an .820" bore would accept a 9/1 gage & would have thus been out of proof even in the exact condition in which it was proofed. A bore above .824 but less than .835 would accept the later 9/2 gage but would have been marked simply as 9 in 1884.
