The problem with V4's knees is that she hasn't got any.

Compare the size of V3's and V4's kneecaps, and you'll see that while V3 has well molded, normal sized kneecaps, V4's are tiny.
(The reason for this is that small kneecaps make a knee appear to bend smoother without complicated fix morphs necessary.)

Anyway, the result is of course that a texture made for V3 WILL look destorted at the knees when transferred over to V4 if you look at them side by side.
It's not that the (re-) mapping is flawed, it's the underlying (V4) mesh that is anatomically not correct.

So I really wouldn't worry, David. You did an excellent job so far.

If you take a closer look at previous remaps, even those that DAZ made themselves, you'll find that none of them is 100% perfect.
Nor are the texture conversions that UTC makes.

And, if  one looks closely, neither are the ORIGINAL UV maps of most figures.
It's just that a texture that is especially MADE for a figure can compensate for the flaws in mapping or modelling, while a remap has to find an "average" mapping that works with a lot of different textures that were NOT made for that figure.

So again, don't worry about the "flaws" too much.