Watch List notes:

The Undated Mule | Elizabeth II (1952-), Undated Twenty Pence, [2008], edge plain, 4.95g, 12h (S.G4A [4631A]), the first currency coin struck without a date for circulation in Britain since the reign of Charles II, a famous modern rarity, lustrous, much as struck, in NGC holder, graded UNC DETAILS ~ RIM DAMAGE (Cert. #6295118-015).

Estimate: £30 - £50