Im sure steve will correct me if im wrong, (which i may well be) but i think SVP either have a supplier that store their media in a dusty enviroment or they have a dungeon like corner in their warehouse.
I had a similar issue about a year (maybe a bit more) back when i purchased a few hundred ritek 8x ice white non-printables from them, (by the way steve get rid of those horrid gold top riteks and bring back the ice whites that have vanished lol they were much better )
First few packs perfect, midway into them weird very fine dust like particles on SOME of the disks which were very difficult to shift. I did consider sending them back SVP are great with returns, dont have to chase them for a refund and no issues getting an RMA out of them (just how things should be).
Having a busted leg at the time though i did relish the possible prospect of wobbling to the post office. In the end i used a very soft cloth and a few drips of water on the few disks from the last few affected packs and carefully wiped them, wasnt perfect but did shift the specs and they burned fine. The disks burn quality have decayed a little since then (as most budget stuff does) but they still read back fine on my PC and dvd player.
I dont blame SVP or the supplier in any way, its just one of those things, i dont think they have a rogue pixie with pixie dust running around, be nice to know why it happens though.