I'm also finding that on the one cake of CMC TY pro's I have; the first 1/2 - 3/4 of the disc is frequently acceptable (or the entire thing if the content is in the 3 gb & under range); the last quarter tends to be unacceptable.
As Each cake of JVC's tended to vary in quality; I'm not totally ready to form an opinion yet; but I am glad I ordered 500 JVC TY pro's while they were still available.
On (at least to me) a related issue: something is going on with the superb entry level Corsair slider Flash Drives. They're likely being discontinued; it's also possible that they just ran low on stock. Unfortunately, I suspect it's the first; Amazon now has an exclusive FOR PRIME MEMBERS ONLY on the slower ultra budget Slider X1's, & it appears Corsair is replacing the "Slider" (no letter) with a much more expensive "Slider X2" with exactly the same specs. I called Corsair, asking if they were discontinuing the model, & was told by 2 departments that it was corporate policy not to comment on product availability. Weird.
I.e. you may want to stock up if you use these drives. They are the only budget Flash drives left that I know of that consistently work well; especially on high bandwidth content..