Interesting to note that a number of the sub varieties identified by Bramah as rare, were never mentioned by Peck. For example the 2a, 2c, 3b, 4a, distinctions between 10b & 10c, 23a, 25c & 26a.
Bramah's book was only ever (as far as I can see) subject to one printing. Consequently, after nearly a century (copyright 1929), remaining often tatty copies are now, understandably, very scarce and very costly. Hence many collectors and dealers are unaware of these rare varieties. Some are especially rare in the higher grades, but seldome attrbuted. Cope and Rayner looked at grade rarity comparisons in their 1975 book, but apart from the 1854/3 - which also, incidentally, is extremely rare in EF and above, according to them - no mention is made of the other Bramah sub varieties referred to above.
The 2a seems to be more widely known about than the rest for whatever reason. Bramah type 17a (the 1854 no colons) was taken forward by Peck, but again, only seldom attributed.
Do we need a new book to raise awareness? - naturally this time with high end photography, including close ups, available