They use multiple media codes so you never truly know who they are actually made by. 1 package can be CMC mediacode and the one right next to it on the shelf can be Ricoh.
They normally buy from the cheapest bidder as far as suppling what they brand as their own, so basically you never know the quality of what you are getting. Rarely if ever is it A-grade, and more commonly is B-grade.
No, not all media is made by the same company. The most respected name in recordable optical discs is Taiyo Yuden, and for a reason. Quality. They invented recordable CD media, perfected it, and have followed suit with their blank DVD’s.
Verbatim does sub-contract out it’s own branded media, but they are all coded the same (MCC 00X). There are 3 company’s that make the discs (CMC, Prodisc, and Moser Bauer India) and they are required to use Mitsubishi dyes (MCC=Mitsubishi Chemical Company) to make the discs with a minimal amount of variation per plant/contracted company.
Basically, not all discs are created equal, and I haven’t even mentioned faked media codes.