Board of Trade Registration Nos. first started in 1842, and are shown in the form of letters and Nos. within a lozenge, and commenced with No. 1.
Registration numbers, in the form of a lozenge, continued without interuption until 1883 - although the format of the lozenge changed in 1867 -and as a consequence there are two separate methods required in order to interpret the details for each period i.e. 1842 - 1867 and 1868 - 1883.
Early in 1884 the lozenge was dropped in favour of providing simply the Rd. No. on its own (aside from any additional Trade Mark), and at this date the sequence of numbers re-commenced with No. 1 - and this effect of repeating a whole series of identical Nos., can be confusing.
However, seems you've solved the puzzle
I believe I'm correct in saying that the uranium lion's foot in your 'molwebbhistorysite' is the example in the V. & A. - it looks like the cabinet in the gallery. I'm well aware that Board members have used museum pix for private webb sites, although my personal opinion is that in view of the help given by the V. & A. and their permission to now use images of their glass on the GMB, we should out of courtesy give acknowledgement to them when this occurs.
Sorry to hear that you walked past a clear lion's foot insulator - realization that you've missed something good can prey on the mind for months, and I find it very difficult to get over losing something good due to being thick - can only hope than I get less thick as time goes by.