Problems still it seems. Attached are pix from Kew archives this morning showing the boat as covered by Registration 39414 dated 11th December 1885, which the Representation book describes as ' ............ pattern of a glass boat' - whether that's just a catch all phrase implying surface decoration only, or perhaps decoration AND the boat shape, I'm not sure. Maybe Ed. Bolton were trying to be secretive in using CLASS 4 for a glass item - who knows.
But, problems come with the other Registration No. 23527 from March 1885. Looking in the Representations book - for March 1885 - Reg. 23527 appears to have been allocated to a completely unrelated design on cloth material - see attached picture. It's possible that 23527 - as applied to Ed. Bolton's boat - may not be from the usual sequence of Reg. Nos., and may be from another series and unrelated to Design Registration, but it appears a coincidence that, numerically, 23527 occurs in the same year as 39414, and is the sort of No. we'd expect from that period. Unfortunately, I couldn't find a Register entry for 23527 - though that may have simply provided a Registrant's details for the cloth design with that No., and I'm still puzzled quite why the time lapse between these two Registrations, if indeed they apply to the same item (the boat).
So, stumped - may go back another time and ask for help.
P.S. For what it's worth both Ray Slack and Jenny Thompson omit 23527 from their lists of CLASS III Registered Designs Nos. - this may have been commented on before and maybe I missed seeing it or perhaps not mentioned previously. Both authors would have used the Registers for extracting number sequence - by far the quickest method of compiling their lists, though not without it's pitfalls.