So not quite a 2:1 ratio in favour of the PT. Thanks very much Ian. Once again, incredibly useful info.
It's odd, isn't it, that Peck made no reference to date width, size, and digit design (for want of a better phrase), except for 1857 to 1859 "small dates". Especially given that date differences prior to 1857, especially 1853 and 1856, are very obvious to the naked eye, and far from subtle. Bramah mentions 1857 (specifically) having a much smaller date variety, presumably because of a report in the Spink Numismatic Circular of March 1895. Apart from that he seems somewhat dismissive of date differences in terms of collectable varieties, because of the sheer number - "innumerable", as he points out.
Yes, Bramah mentions Henry Christmas's work "Copper and billon coinage of the British Empire" (1864) in his bibliography. Something he says at page 108 seemed slightly odd in view of the fact that by 1929, 60 odd years had passed since demonetisation of pre 1860 copper. Yet he says: "......it is very doubtful if any casually-acquired hundred specimens would in practice contain any examples of those dates to which 1 per cent is allocated. The simple reason is that the scarce dates are retained by collectors and will not be found in promiscuous assemblages". Where would anybody have "casually acquired" 100 specimens in 1929? Certainly not from change. By definition they would only be available for sale as collectors items, or the odd few in jam jars etc. Of course, I'm pre-supposing that huge bagfuls of random copper coins weren't available then, in the same way as they are now for pre decimal bronze.