Lots of information in this thread. Most of it is accurate (unlike digitalfaq where half is accurate, 20% is wrong, 20% is misleading, and 10% is quite strange.)

1) Memorex made CD-Rs in a plant owned jointly with Ritek.
2) The media code is issued to the owner of a stamper who submits samples to a governing body for approval. The code represents the stamper owner, the dye used, the stamper (groove geometry), the format, the rated speed, and the manufacturing process.
3) Discs manufactured with different stampers with different groove geometry and different processes can behave entirely differently even with the same dye. The dye is delivered as a powder, so the solvents and formulae, pump systems, pressures, and spin coaters make a vast difference in performance even with the same powder. The dyes that react to the 635/650 nanometer wavelength are cyanine, metallized azo-cyanine (sometimes just called "azo" or called "metal chelate"), and oxonol. There are multiple developers of these dyes.

The point above is excellent. There is no such thing as a good quality MID or a bad quality MID. The MID is a code recognized by modern drives whose cost-cutting has eliminated the ability to read the field codes on the discs and adjust themselves properly. It appears that these MID codes are used by some drive manufacturers to actually make some brands look bad for the benefit of other brands. Some great quality discs produce poor recordings on great quality drives simply because the firmware engineers failed to or decided not to support a particular disc.