Numerically the first card in my personal collection is A.0121 'Aberdovey Promenade' with this image dating from 1973 (or earlier). Earlier cards exist for Aberdovey such as ...

but this 'Newcolour' style card was posted in 1952 which was 3 years before the start of the numbering system. This may well have become A.01nn since many pre-war and early post-war images were allocated numbers before better or more modern images could replce them. Additionally all the 5 images which are part of this multi-view would also have been cards in their own right.