Yeah, proved before the 1887 rules executed, and Brown's table says 1890. He indicates that Henry's records seem more jumbled than most, but this kind of thing with British guns in general isn't at all odd. Even if the Day Book page for that rifle says 1890, it's obvious that it was proved well before then.

It was normal, and still is, for a year or two to pass between the date of proof (conducted when the gun is a long way from finished) and delivery. Even longer periods aren't that strange. For example, the legendary East African professional Philip Percival ordered a new pair of .450 No. 2s from Joseph Lang in 1927, which his family sold at Bonham's last year. The pair were assigned consecutive numbers from the current range when the order was received, and were delivered late that December. The rifles were built in 1907. I have a William Evans DR in my notes built in 1921, and delivered to the original owner in Bulawayo in 1948. A friend has another Lang DR, built 1923, assigned a number in 1946, and delivered in 1952 - by which time the cartridge it was chambered for was obsolete!