I've read the reviews both on German and US sites - the US ones are very favourable (for a separate gel foundation as they didn't have a set). On qvc.uk there's a mixed bunch of reviews.
we'll probably never know
as QVC does not post the ingredients, at least not locally
but i suspect that the formula varies
i.e. individual gel foundation, lets say is original Doll 10 formula
then TSV formula is different as QVC demands a certain price point/volume
so formula gets amended to make it cheaper to produce, incl possibly more fillers etc
but they still sell under the established product name
and they quote all the good reviews from original formula
hence you get comments like this on the German site
'i applied the gel foundation i already had one on one side of my face
and the TSV gel foundation on the other
and there is huge difference, no coverage etc
so i am sending back'
it is all smoke and mirrors with QVC imho
(even though they are not the only ones ...)