The Memorex 12x and 10x discs that I've used are readable, too, but the write quality on them is terrible. Here is the ATIP of one of the Memorex 12x CD-RWs:
Drive Type = CD-RW
Disc Type = HIGH SPEED CD-RW
Material = Phase Change
Lead In = 97:25:30
Lead Out = 79:59:73
Nominal Capacity = 702.83MB (79m 59s 73f/LBA:359848)
Manufacturer Maybe = Infodisc Technology Co., Ltd.
Smart-Burn Speed Limit = Wrt(10X),Rd(40X)
Here is a KProbe scan of this disc written at 10x in an LTR-52327S:
The recording quality of these discs is also very bad when written on a NEC 16x10x40x CD-RW drive (I forgot the model number as it isn't mine).
In contrast, here is a 12x Philips disc written at 12x in the same drive.
Drive Type = CD-RW
Disc Type = HIGH SPEED CD-RW
Material = Phase Change
Lead In = 97:26:65
Lead Out = 75:00:00
Nominal Capacity = 658.89MB (75m 00s 00f/LBA:337350)
Manufacturer Maybe = CMC Magnetics Corporation
Smart-Burn Speed Limit = Wrt(12X),Rd(40X)
Interestingly, the Memorex RW has been written and erased far less times than the Philips one.