delayed reply not a problem

Regarding your lamp - a similar square pressed foot - sometimes domed, occasionally terraced, is found on only a rather narrow range of drinking glasses - seen most frequently possibly on English rummers 1790 - 1820 which have a short capstan stem and lemon squeezer foot, and because of similar features on your lamp I'd suggest your lamp base might be somewhere in that date range - correct me if I'm way out. Mostly these rummers have a single 'collar' immediately below the bowl, but double and triple collars/mereses do occur. Other than rummers, square pressed feet are found on monteith glasses, and again they are vessels with rudimentary stems and lack finesse.
The problem here seems to be one of how the experts interpret that feature immediately under the bowl - whether it's thick as in an 1850s collar on a wine glass, or thin as your wafer.
Bickerton uses the word collar to describe such a feature (under the bowl) during the entire C18, whether it's thick or thin, and his index doesn't include the word merese.
Tim Mills uses both descriptions - merese and collar .................. this author says of one rummer with a square, domed, lemon squeezer foot, inscribed with the date 1799 - "....... a rounded merese to add strength between the bowl and the stem, and square foot" - and this particular 'merese is truly substantial - what I would call a collar.
I'd suggest, generally, that if the feature is fine in proportions then the word merese is more appropriate - if it's thick and heavy in appearance then perhaps we should say collar. Whatever, in its finer form for quality wines it's a flattened disc often with a sharp outline to the edge - not a lot unlike a bladed knop.
Pix attached showing some second half C19 wines with and without collars - and some of which I'm uncertain as to description - these are run of the mill glasses, inexpensive and simple and don't think we would justify calling the feature here anything but a collar.
I'm clueless as to terminology for oil lamps, but think in the U.K. we might use the word reservoir instead of 'font', but I hate to be dogmatic, and since you obviously collect these things you may well be correct and likely I'm wrong - was there original a water filled globe as in lace makers lamps, or just a refractive type of shade? The panel-moulding is almost wrythen in appearance. Hollow blown knops are seen on high end goblets and wines from the late C17- but if yours are blown then IMHO I wouldn't call then collars - knops instead I'd suggest.
Are all three knops/collars blown - can't see from your picture.