question about potatoes and viruses...again

There was some vigorous debate a while ago regarding the wisdom of allowing potatoes to volunteer in the same spot indefinitely.
I got freaked out about viruses as supposedly even really healthy potatoes will eventually succumb and in my little garden, that means solanums would be out.
On the previous thread, there was plenty of "I've had my potatoes in the same spot for ever and they're fine" type comments, with one or two people arguing strongly against it.
I have spuds everywhere as I never manage to dig them all. We're talking polyculture+
The plants are very healthy and have been producing potatoes since early spring (bear in mind I'm in the Southern hemisphere...)
I planned to dig them ALL after they produced this season, but before I spend a lot of effort getting rid of things that seem perfectly fine, I'd like to hear from people.
Has anyone actually had a potato virus? I really want to leave them be, but I REALLY don't want blight.

i had. but because i bought shit seed potatoes. find somebody whose growing good healthy sort for a while and just take seed. the one i had was from holland and had spotty rotenning. i lost almost all of it.

I haven't been doing it for long, so I'm just going from a book I read (not sure which one, maybe Deppe's Resilient Gardener?) here.  Anyway, the apparent case was that the potato virus ends up reducing yields as it accumulates.  I seem to recall that it wasn't a total loss, deformed mutant potato sort of situation, but was rather a case of getting somewhat less out of your potato patch after awhile.  I'll happily defer to others with actual long-term experience though.

Not really long term but I've had potatoes in the same spot for 3 or 4 years. They're in an area I don't grow things in regularly. The plants always seem fine and the spuds too. I don't know about yields as I haven't taken any notice. This year I plan on digging some and planting them a bit deeper as most are near the surface now. These particular plants produce plenty of seed, true seed I mean, from fruit, which I have grown. They produced nice spuds. I've sown more for this season.