No, Frank, I chose my words carefully here, and deliberately used
date the pattern.
There are many dates that can be associated with a product, most of which we don't usually know. The best date of all is the pattern date, i.e. when the product was given a factory pattern number, as this is a strong indication that this is the moment when a product changed from being in development, through the first idea, then experiment and trial, to become an accepted factory product.
We are fortunate that Sowerby used a single sequential system of pattern numbering throughout the factory's existence. When this is combined with other dating evidence, it enables us to date patterns with a high level of confidence, particularly when that other evidence is plentiful, such as during parts of the late 1870s and 1880s when many designs were registered. Hence my two month high degree of confidence window for this particular pair of pattern numbers.
The use of the word
introduction has two problems. It dilutes the quality of information. Also it hints at a launch date, about which we have much less information.
My apologies for not explaining all this earlier, but I didn't think it necessary.
Bernard C.