Problems beginning to surface on old backed up karaoke discs

[Videopro]

I know mitsuis are the best blanks out there & that's all I've been using for the last few years, but before I owned a plextor drive & used mitsui's I had an HP burner (8100) and sony blanks. Now it seems like the old backed up discs are not playing back as well as they used to. I get alot of letters being left behind on the screen. If I extract the disc which is not playing very well to my computer's hard drive with the plextor drive & burn another copy with MTU all is well again. My player plays anything burned on a mitsui fine along with everything that is original. Could there be a problem with the old blanks or the burner that made them? Higher number tracks act up more than lower number tracks. These did play well at one time. Thanks for your help.