Prodisc s03 varying results

i have a 50 spindle of prodisc s03s, and i’ve noticed that most of the discs i burn now i have a very high error rate toward the end and are almost unreadable. these are the discs only at the bottom of the stack. the past 30-40 discs i’ve burnt have been perfect, but these last few are giving me lots of problems. is it possible that within a spindle of prodiscs there can be bad media? these are only marginally better than the sonic 4x i had before. i’m not overspeeding any of these discs, either.

so far, this is what i’ve found: ritek g04 > prodisc s03 >= sonic 4x (longten001)

i’m trying one of the GQ discs at fry’s made by LEADDATA and some of the best buy 8x TY Fuji discs later.