the Board's archive shows the canoes you mention, also dishes with the usual 212684 decoration but with four compartments, so this tri-form shape looks to be new for the Board's Davidson archive Anne. Either I can't remember, or I've not previously looked at the factory drawings at Kew for this Registration, but I've no idea off-hand what the shape of the original factory Registered design was for 212684 - always a chance it was the boat. Unfortunately, the books don't help with any cross reference as to shape/Rd. No. so can't work out which shape came first.
Sheilagh Murray shows a example of the boat in yellow pearline (plate 55 - but omits the Rd. No. both on the plate and in the text), but the lady's text - in reference to this boat design (which we must assume is 212684), makes for very interesting reading - have to say I'd not read this previously (page 64).