V4 was a base character. Other Generation 4 characters were morphs of V4.

For Generation 7, Genesis 3 is the base character and is free, although the morph packs to create a variety of features is not free. Victoria 7, Eva 7, Karen 7 ... are custom morphs of the Genesis 3 base. These DAZ characters each have custom UVs for their skin. These UVs are suppose to be optimized for their body shape. I can see this with an extreme body shape, but the benefit with the normal body shapes is modest. In any event if you purchase Victora 7, then you can use the Victoria 7 skin on any Genesis 3 based character shape. You can use the Victoria 7 UVs on Eva or Karen body shapes, even though the skins for those characters use different UVs.

While Victoria 4 only supported one UV set, Genesis 1, 2 and 3 all have multiple UV support. Genesis 3 comes with support for the Genesis 3 base female UVs. If you purchase Victoria 7, you get V7 UV support on any Genesis 3 character shape. Now the only skin I know of that uses the Victoria 7 UVs is the Victoria 7 skin. Even the other characters that come in the Victoria 7 bundles all use the Genesis 3 base female UVs. For generation 7, characters that require Victoria 7 means they use the Victoria 7 body shape morph as part of the body shape. If you do not own Victoria 7, you can still load the character. There will probably be an error about missing Victoria 7 morphs and the body shape will be different. The skin will work because it uses the base female UVs.

In generation 5 and 6 this was not always true. Some other characters that said they required Victoria 5 or 6, used the Victoria 5 or 6 UVs. You could not load the skin correctly unless you had the Victoria 5 or 6 characters. As far as I know PAs have stopped doing this in generation 7, but it is always possible that a character will be released in the future that uses the Victoria 7 UVs.