1879 Shilling KM#734.4 "No Die Number" Variant

Both Spink "Coins of England" and Bull "English Silver Coinage" give the No die number version of the 1879 shilling as MORE common than the die number version.
Spink values No die number in Fine at £12, with die number at £20.
Bull gives no die number rarity index N for Normal, with Die Number as R2 for low end of rare scale.
This assumes both are Fourth Bust, which is difficult to be certain with the level of wear on the example. A Third bust version of 1879 Spink notes: "Uncertain to exist as Normal or Proof".
I hope that helps.

If you look on ebay nearly all the so called rare 3rd head being offered even by knowledgeable sellers are 4th head with a few of the more recent unrecorded 7B pairing . I think that is probably where the confusion is If its reverse B it must be 3rd head and has probably been attributed wrongly for years. Also for the same 1879 Shilling there is an extremely rare variety with a GBATIA error