Here are images of the serial number stampings of three Anglos and two Englishes that I would consider appear to have been made by the same maker, and describe as "Tidders" - though we could definitely do with reports/photos of more instruments with similar features.
The earliest one, baloo's 20-key Anglo labelled J. Wallis, Euston Road, London, "has several serial numbers - 372, 378 and 399 all in different places" with 378 'printed' on the righthand reedpan (though we could do with a better image of it, as well as pictures of the other numbers), below:
Wayland's 20-key is numbered both 921 and 924:
But the one Jim saw in Helsingør Library, and photographed, has only the one number, 3116:
The English-system ones are stamped R and L in the right and lefthand ends, in addition to the number. This is Dave Elliott's one, number 3459, which sparked this thread:
Whilst this is from the eBay one, number 5236:
To my eyes those numbers all look like they were made with the same rubber stamp(s), which (along with other features) would seem to confirm that they were made by the same people.
Stephen, I concur in the number stampings, and I have just checked the 'R' stamp on mine, and it is the close cousin, if not twin of the stamp on 5236 above.
Edited by d.elliott, 12 March 2014 - 06:04 PM.