It's not really a write speed lock. The drive will only offer higher write speeds if it's confident that the write strategy it's going to use is appropriate for the particular disc you've inserted.
I've got some old Kodak CD-R media left that most drives can write at 24x, and the NEC media list says should write at 24x. In fact, I can only write it at 8x. Still - it does seem to write OK, so I'm grateful for that.
The Kodak media was, at the time I bought it, some of the best CD-R media about. However, it's been hanging around here over 2 years, and most people seem to say that CD-R media has a finite life before it's written. I'm therefore very aware that it's likely not in perfect condition.