I've had the excact same experience as you have, with disks becoming "unreadable" (going from perfectly readable to having read errors) the moment I apply a label on them.
I've labeled hundreds of cd-r's, and never had a problem with any of them due to it. If anyone had told me I'd ruin my DVDs (before I discovered it myself) I'd just laugh at them
I started to realize I had a problem when a friend a mind borrowed a pile of DVD-Rs to make a copy, and when he returned them he said many were unreadable. Eventually I created a few disks which I ran the rpm test in dvdinfopro tens of times, and over several days, just to see disks were "perfect". I then applied a label using a toolkit, I have several kits here, and packs of labels. The result was very predictable, the disks would deteriorate, start with speed drops and end with read errors.
I experienced this with Princo 4x dvd-r, Princo 1x dvd-rw, Traxdata 4x dvd+r (ricohjpn01). Two cheap and one good brand, all disks acted the same, and they acted the same in the nec 1300 (now replaced with a 2500), Plextor 116a and my Daweoo player.
I can't stand the idea of having dvds with my ugly handwriting instead of a good looking printed label, so I said fu** it and bought 250 8x ritek r03 printables. I've received the disks, but not upgraded my printer yet
It seems the definition of a "coaster" very wildly. I define a coaster as a disks I can't read back perfectly in my Plextor OR a disks that skips in my Daewoo. Many seem to label anything that doesn't skip in their tv set dvd player as a "good" disk, but the fact is that dvd players have a number of routines to overcome dvd read errors/imperfectiosn. I seriously believe many that claims to have hundreds of perfect labeled dvds have hundreds of coasters (by my standard, not theirs).