>Grape juice is absolutely not normally grape juice plus possibly sugar.

How sure are we on that? It has been a while, but I recall something like Welch's tasting like grape juice.

https://www.welchs.com/juices/100-percent/concord-grape

Seems like theirs actually is. But that’s also likely why it costs more.

Apparently even walmart's great value grape juice that's half the price is apparently 100% grape juice. Given how much Welsch's seems to be pushing the grown in America angle while a location isn't mentioned at all for great value, I think it's a fair bet that they've found some source of super cheap grapes somewhere to let them get that 100% grape claim

Welch's purple grape juice is concord grapes: "In the United States, 417,800 tons were produced in 2011.[3] The major growing areas are the Finger Lakes District of New York, Lake Erie, Lake Ontario, Southwestern Michigan, and the Yakima Valley in Washington.[4]"

You can use it to make wine just fine, if you're in to that sort of thing.

If i had to guess the white grape juice is whatever the green seedless variety in california was for decades from the late 70s on.