Note that the 1874 is a Sowerby pattern number, not a date. Sowerby pattern numbers are sequential, so caught up with and overtook the date in 1886.
The 1874 boat was a registered design, No. 42947 of 10 February 1886. I know of at least four sizes, 4½", 10", 12", and 16" (Thompson p25), and I am sure I've seen an 8" or thereabouts.
Sowerby registered a dish in the same 1874 pattern a month later on 11 March 1886, Reg. No. 44659. Possibly the boat registration was too specific and excluded other shapes. The archives at Kew might provide an explanation.
Bernard C.
