I was looking up penninite (pennine) for someone, and came across "pennite" in Greg and Lettsom. Penninite and pennine are both synonyms for clinochlore. Pennite is/was apparently a carbonate. See page 58 of Greg And Lettsom.
There are a number of older unused nomenclature for this supposed species "hydrodolomite", largely described as a mixture of Calcite, Dolomite and Hydromagnesite. Pennite (Hermann), Hydromanganocalcite (Hartmann), Hydronicklemagnesite (Shephard), Kalkmagnesit (Hausmann).
There are many examples of old nomenclature which are also not included here on mindat, such as the variable named vermiculites like Perhamite, Jeffersite, Philadelphite etc . .
Occasionally some that found more general use, like "Lancasterite", a mixture of primarily aragonite with brucite, do get included, but I would think some lines need to be drawn given how many specious identities were bandied about in times past. I've a particular interest the history and mineralogy of Woods Chrome, and have for many years, yet Pennite was even overlooked by myself as it seems to have found little use.
I'd have to leave this up to the managers of course, but were we to go about including every mention of the many illegitimate identities, we've a ton of them yet to add to the list.
Yes if you go through old books there are many hundreds of obsolete names missing. I periodically add some if I think they have been used relatively recently, but it's another big job on a long list. If you give us all the details Steve I will add it.