Welcome to the forum
Not sure about the -R as I use +Rs mainly, but the Prodisc-made Verbie MCC004 - several 25-packs - that I've used, have held up well so far. The only thing I found were a couple of lemons that failed to burn halway through in one of the spindles. But that can happen with any manufacturer or brand, be it TY, Verbatim...
I have a couple of Samsung drives that burn the MII ones beautifully, and on those drives, the Prodisc ones burned just as well, and in a few cases the Prodiscs even burned with "prettier" scans than my CMC-made ones.
As for when they start to detreriorate. I have TYG01 sitting here, both burned and blank, from about 2004. The burned ones are still going strong, and I would hope for the many of us who have older or rare media sitting in storage, that they'd last a fair while if not burned. From what I have seen personally, it appears to be burned ones that go South more often than unburned ones. I also have several spindles that I use for review/testing purposes, and the packs were opened a few years back. These still are fine when I go to use them.