SG list quite a number of postal fiscals, i.e. revenue stamps that were authorised for, and used in the post.
As far as I know they only list adhesive stamps of this kind.
I see my old SG GB Queen Victoria Specialised catalogue lists in detail quite a few revenue stamps that were used for postage, especially inland revenue and draft stamps but it also says many more types were accepted as well although they mention some of these other types without giving a detailed listing.
These references seem to refer to just adhesive stamps, whether surface printed or embosssed, rather than handstamped stamps like the ones here but I suspect these handstamped stamps were accepted under the same regulations.
It would be fascinating to learn more about this.
Thanks for sharing this topic.
