There are three (or possibly more) terminologies for dies and/or types. Fortunately, they don't overlap. Here they are:
Die 1A = Die A = Type I Die A Die 1B = Die B = Type I Die B Die 2 = Die 2 = Type II
There are also three watermarks: [Imperial] Crown, Simple Cypher and Multiple Cypher, some of which also exist inverted.
It looks as if your album also has spaces for two or more shades of the green and red inks.
Probably no two collectors will agree about how many stamps are needed to make a "complete" set of Downey Heads.
I don't know if it will help you or confuse you further, but here's a listing of the eighteen Downey Heads that I find sufficient for my collection. (SG Specialised numbers first, then SG Concise numbers, then descriptions):
N1, 321/323, ½d Green, Wmk Crown, Die 1A N2, 324/326, ½d Green, Wmk Crown, Die 1B N2a, 325Wi, ½d Green, Wmk Crown Inverted, Die 1B N3, 334/335, ½d Green, Wmk Simple Cypher, Die 1B N3a, 335Wi, ½d Green, Wmk Simple Cypher Inverted, Die 1B N4, 338/340, ½d Green, Wmk Crown, Die 2 N5, 344, ½d Green, Wmk Simple Cypher, Die 2 N6, 346/348, ½d Green, Wmk Multiple Cypher, Die 2
N7, 327/328, 1d Red, Wmk Crown, Die 1A N8, 329/331, 1d Red, Wmk Crown, Die 1B N8a, 329Wi, 1d Red, Wmk Crown Inverted, Die 1B N9, 332/333, 1d Scarlet, Wmk Crown, Die 1B N9a, 332Wi, 1d Scarlet, Wmk Crown Inverted, Die 1B N10, 336/337, 1d Red, Wmk Simple Cypher, Die 1B N10a, 336Wi, 1d Red, Wmk Simple Cypher Inverted, Die 1B N11, 341/343, 1d Scarlet, Wmk Crown, Die 2 N12, 345, 1d Scarlet, Simple Cypher, Die 2 N13, 349/350, 1d Scarlet, Multiple Cypher, Die 2 |