Penny Red From Plate 75 ?

Thanks, Geoff!

The "W H Smith and Son" stamp has what is called an underprint and that was a security measure for companies who used lots of stamps in their business. It has similar properties to perfination.
Plates 92, 97, 103, 109, 119, 121, 124, 131, 134, 147, 152, 164, 169, 173, 174 and 183 have been found with this underprint... so you maybe can identify it if you magnify.

Very interesting, I never would have guessed that!

I'm glad you mentioned perfination, because I found a "holey" stamp about which I was wondering (subject of separate thread).

I've the same question.

On the left looks like 191. On the right, I see 193.

A very useful resource is Billig's Philatelic Handbook volume 34, part 1, The Encyclopedia of British Empire Potage Stamps, Great Britain and the Empire in Europe, page 170 has a list of the plates of penny reds with check letters in four corners. Here is a citation: "plate 69, 70, 126 and 128 were rejected as unsatisfactory, and 226, 227 and 228 were not put into use. The rare plate 77 was badly spaced and most copies known are off centre." I would still take one of those off-center copies! The same information is to be found in the Stanley Gibbons Great Britain Specialised Catalogue Volume !, pages 132-133. Both are fairly easy to find on the used book market for $20-$30 apiece.