yes, think you're probably correct - it sounds to be a a common sense expression equivalent to 'overlay'. Don't know about your side of the pond, but Europeans would be likely refer to a piece with this appearance as 'cut to clear'. The traditional means of making drinking glasses with shapes similar to this is by means of a three part construction - bowl, stem and foot - it's possible here that the clear bowl was cased/overlaid with the opaque colour, before being attached to a clear stem, and finally the overlaid foot attached. But I'm speculating of course, though to overlay a bowl once it's attached to stem and foot would be more difficult.
With the glass in its completed form the bowl is then 'cut to clear' - a decorative technique I'm sure seen more commonly on the Continent of Europe (particularly Bohemia), rather than within the U.K., though it was a process used everywhere.
Nice pieces if they're all yours. This doesn't solve the other contradiction of translucence versus opacity - and we may never resolve that one (from the book).