Ritek has a lot of production facilities which have big differences in quality. Most production lines of Riteks are makeing not so good discs.
Now the compannies I said use allways the High Quality disc's made by Ritek and which do perform in most test's better as most brands. However most other compannies like Philips,Basf,Traxdata,Arrita are using the other lines which do make the not so good discs and which are in most casses even more worse than most Prodisc disc's.
These are probally the ones you have used.
These days everything get's more complicated. Since for a few years ago you could just say by the manufacturer how good disc's where. But today with Ritek and Taiyo Yuden and most other manufacturers you can't trust that anymore.
So the best option is still to buy disc's which where made by the manufacturer. Acer, Mitsui, Verbatim, Kodak are 4 brands which allways score constant in most test's and still do make there own disc's.