Asked in British Coins
Why are 1990 1991 and 1992 silver Piedfort One Pound coins so rare?
They are not rare, they are nonexistent. The Royal Mint did not mint any 1990, 1991 or 1992 Piedfort silver Proof One Pound coins.
In years when Piedfort coins are minted, the Royal Mint only produces quantities they think they can sell. There is not a huge market for non-circulating legal tender coins of relatively large cost, and quantities of 5,000 to 15,000 Piedfort coins of any given denomination are what is most commonly produced.