Sounds like they've been in the ground for over 70 days?
And it does sound like they're done.

If you leave them in the ground the curing process will proceed (as long as you don't have voles or other under ground critters, in which case the *eating* process will proceed!) The skins will harden and they'll store better.

I also find that potatoes will harden their skins once dug, as long as the vines were really done.

So, my recommendation would be to leave them in until the vines are really dead. In the mean time, start eating a few to make sure there isn't any underground damage going on. Then get them good and dry for storage. YG's store so well, I'm sure you'll be able to keep them and not have to eat them all now.

Why they made fruit, and why they died back before 90 days, I will leave to someone else to answer -- mine sometimes make fruit, too.

I got fruit on my potato plants last year too! They were on Russian Blue potatoes.

I got fruit on my Yukon golds this year too! I don't recall that happening before.

the fruiting happens once in a while, so you might see it one year, and not the next. Most, if not all of mine fruited this year. My vines are dying back and are nearly dead. I dont see any reason why you couldnt store them, if they're cured properly, or why you couldnt eat them

My potatoes usually fruit. But except for new potatoes, I wait quite a while between fruiting and harvest.

My Yukon Golds have seed balls too this year. They mature sooner than many other varieties.