Your assistance is much appreciated, Paul.
I'm not really surprised that Cottle doesn't allocate pattern numbers to Sowerby RDs 350086 and 350093. Neither design is for one of the small, decorative pieces that appear in the 1882 pattern book. In fact, both designs are for pieces of domestic tableware that are lurking in the Sowerby pattern book XI from 1885:
RD 350086 corresponds to an octagonal dish, pattern 1486 (or 1486 1/2[half] for the smaller version) shown on page 27. No indication in the pattern book that this is a registered design.
RD 350093 corresponds to a lidded butter dish, pattern 1491, shown on page 7. Indicated in the pattern book that this is a registered design.
I don't have reference photos for either pattern 1486 or 1491 - does anyone have photos to show, please?
Fred.