1937 Great Britain Silver Threepence varieties
The George VI silver threepence was struck with two very similar reverse dies between 1937 and 1945: the main difference appears to be orientation of the I in IMP in relation to the rim denticles. On Davies reverse A the I in IMP points at a rim denticles and on Davies reverse B the I in IMP points between rim denticles (p99, Davies, British Silver Coins Since 1816, 1982).
In 1982 Davies reported that both reverse A and B were used to strike 1937 threepences though notes that the usage of reverse B is unconfirmed (p100, Davies, British Silver Coins Since 1816, 1982). In 2010 Groom repeated Davies' observation that the variety was unconfirmed (p104, Groom, The Identification of British 20th Century Silver Coin Varieties, 2010).
It seems unlikely that the 1937 reverse B silver threepence (Davies 2231) exists - the lack of any reported examples between the publication of two books on the series, and the lack of any attributed examples at auction suggest it will probably remain unconfirmed.