Intiguingly I have been carefully examining a lens engraved Howard Grubb and which I am thinking is probably from the 1990s )certainly post 1883 but more likely 1895+). Surprise, surprise it too has 'rice writing' on the glass of 'Grubb Patent serial number'. Also intriguingly, it looks very much like one of Thomas Grubb's 'A' type Patent lenses but fitted into completely different brasswork and with a rotating stop mechanism at the front. If I'm right then this would suggest that Grubb Patent lenses were on sale for around 40 years even if only in small quantities.

Also FWIW I have tracked around 150 Grubb surviving lenses to date although not all are complete and some details are scant to say the very least. I also estimate that complete production from both Thomas and Howard is probably less than 4500 in total, or which ~300 were from Howard.