Did a sample of Verbatim DL disks from my rather small collection of dl burns. I scanned ten disks, one of which I knew to be bad going in.
This is the result from the first one, a disk burned 3 yrs ago:
You'll notice the 521 PO errors. This disk is completely unreadable.
Here's the second bad one, burned just this month. 19141 PO errors, also completely unreadable. ISOBuster just laughs at me when I try to extract anything from this one. And yes, I tested this just after burning to see if it would play then...it played back just fine.
Going back a few years further, we get this gem:
This one still plays back ok, but is obviously much worse than my original scans, (unfortunately those have been lost over time).