Interesting. Don't collect Britain, though I had a bunch of Victorias that I sold via
ebay last year. Never had anything older than 1880 (except for a couple of penny reds) so was unaware how they printed the plate number on the stamp like that.
As a side note, looking at some of the images of the stamps I sold, there were a couple of gems in there. Had the makings of a nice Victoria GB collection. Shoulda coulda woulda I suppose.