Neat stuff, Rod.
Thanks for posting 22071 . . . it wasn't on TheList, but it is now.
Ahead of you on TheList are 19900 & 19901. While 19900 is listed as having a 6-1/2" barrel, it "letters" as a BKH3 . . . and 19901 is listed with a 10" tube but also "letters" as a BKH3.
Then we have 20316 & 20317, both 4-5/8" guns.
Also on TheList in that range are 21691 & 21692, both 4-5/8" guns, as well as 21712 & 21713 which are engraved 4-5/8" guns, and 21911 & 21912 a pair of 6-1/2" guns.
A little further down the list we have a pair of 6-1/2" guns, 22291 & 22292. One of these "lives" with a Forum member.
There are several "pairs" earlier than all these, including a few in the ROSS group.