Recently I purchased the above Ally Sloper stereocard. In the bottom left hand corner of the postcard it reads "1727 ALLY SLOPER BUYS A TRICYCLE".
I have seen another Ally Sloper card go on sale before, but I cant seem to find a picture of it. It featured Ally Sloper standing on a box with someone at either side of him, the box reading "Ally Sloper's Half Holiday" (promoting the comic he appeared in).
I also managed to find another Sloper stereocard online, which reads "1726 ALLY SLOPER PHOTOGRAPHING" (seen above).
'1727' is probably the number in the series, although I doubt they made over one and a half thousand different cards. If anybody can shed any light onto them please let me know!
Another one of the Steroeocards has appeared on eBay (the tricycle one, as seen at the top). The seller has supplied some of the publisher information. The cards were published by Stringer's Stores, at 22 Cross Cheaping, Coventry.