I think I've found what happens with writeable DVD's and why they stuff up........
If you look at a 'Pressed' or commercial DVD movie disc, it appears bright silver, presumably a metallic medium that is a good conductor of heat.
The Recordable DVD's that we use have a Blue Die plastic medium that does'nt transfer heat as well as the metallic medium.
This disc heats up whilst being played, and as they are very sensitive to temperature, may start to miss-read the Data on the disc after about an hour into the movie.
By sticking a big label over the top of the Disc, it actually acts as a blanket and prevents the heat being dissipated, and makes things worse. I found that allowing a disc, that was playing up, to cool down for 10 minutes or so, I could still go back and copy the files that had previously been 'faulty', to my hard disc folder for a rewrite.
Printing directly onto the disc should not interfere with the heat dissipation and should result in more reliable playback , and since I have started using 8cm paper labels which only cover up the centre of the disc, my results have been extremely encouraging.
see www.mediafood.com for 8 cm labels.
I will be interrested to see if any changes occur when the discs age.
I still think you need to use the DVD makers recommended media, and a slow burn with verification to ensure best possible results.
NOTE: I have just removed the cover from my DVD player and placed a fan on front of it whilst playing a movie (complete with label) and had no problems at all which seems to validate the heat exchange theory. Next move will be to install a fan within the DVD case.