Unfortunately Sowerby pattern book XV (1895) does not indicate which of the patterns are from registered designs (though some are, indeed, known to be from registered designs).
Simon Cottle’s ‘Sowerby – Gateshead Glass’ links many Sowerby design registrations to their pattern numbers, but pattern 1877 is not among them.
The Glass Queries Gallery athttp://glassgallery.yobunny.org.uk/thumbnails.php?album=1001
is dedicated to photos of Sowerby pieces numbers organised by pattern number (and correlated, where known, with their registered design numbers), but Sowerby pattern 1877 is not shown.
I still have photos of lots of Sowerby pieces to add to the gallery, but pattern 1877 is not among them either. In fact, the Thistlewood Vol. 3 CD-ROM is the only place that I can remember that shows photos of pieces in the pattern.
Although the Sowerby pattern numbers from known registered designs tend to follow
a broad chronological sequence there are quite a few anomalies that fail to conform to the sequence numbering. Having said that, here is a brief list of known Sowerby patterns from around pattern number 1877 correlated with their registered design numbers :
#1874 RD 42947 registered 10 February 1886
#1896 RD 54314 registered 18 August 1886
#1901 RD 48909 registered 11 May 1886
#1913 RD 56963 registered 23 September 1886
#1921 RD 64086 registered 22 December 1886
So, if Sowerby pattern number 1877 pieces are from registered designs, then they are reasonably likely to have been registered in 1886.