hello Robert - I suspect that Tim Mills book is available only from him direct, via the link shown earlier in this thread.
Nice collection of licks - they seem mostly to have this general shape - there appears not to be a great deal of variation. Looking at my few, some are without any visible seams (vertical) - some have two mould lines - but can't say I've seen any yet with more than two lines. Assume you're speaking of the horizontal lines - although I personally wouldn't have thought that these had any connection with the capacity of contents - I've always assumed that these things were simply filled level with the rim - I can't imagine there was remotely that the buyers would get any guarantee of an exact amount of ice cream. Most licks are without any decoration, other than a feeble moulded attempt at an imitation collar or merese where the bowl joins the stem.
You may be correct about the date you're suggesting - not easy to assess in view of the lack of book information on these things - other than to say that those pieces showing a Y or T mark (left by the shears when severing the pontil gob from the underside of the foot), will probably date to somewhere around 1870 ish to perhaps the end of the C19. Apparently they were banned in London due to the assumed problems connected with tuberculosis, but may have continued in use elsewhere for some time.......... maybe those with an entirely moulded shape date more to the end of this period.
I've attached pix of two of mine about which I'm not sure - always possible that some salts might be confused with licks. The taller example has a typical lick shape to the inside of the bowl, and might be a 4d or 6d lick (pre-decimal Sterling) - what do you think?