Reported available writing speeds I think also depend on the discs themselves, not just the drive.
A good point. It is the combination of the drive and the media that determine which Read and Write speeds are available.
I tend to use the free version 8 of
Nero InfoTool to check drive and media capabilities, because it separates out the Drive and Disc capabilties. It is a bit old now though, and later versions tend to have adware in them. There is a version 11 available
here which I think is okay, but I haven't installed it so can't guarantee that.
Then there is the ever popular
ImgBurn, which is up to version 2.5.8.0, although last updated 16th June 2013!
Note that Norton 360 tells me the ImgBurn site is unsafe, but it is fine. ImgBurn has a Discovery Mode that will show you the available write speeds and other data. Information about the drive is found under Tools>Drive>Capabilities. The results are the same as Nero InfoTool, which is comforting, and ImgBurn is faster to analyse the drive and disc, and display results. It is just a bit more complex, and of course is a burning tool as well as an information tool.
Note that both applications require a blank CD to be in the drive to determine the available speeds, and both show a much shorter list of compatible speeds than JRiver MC shows as available speeds. On my drive, for example, 1x is not shown as an option, and for that reason I wouldn't use 1x on the Drive/Disc combination. I would use one of the supported speeds, for example I tend to use 24x, but 4x is also available if I want to do a slow disc Write.
It is possible for optical discs to "go off" over time, depending on their storage, quality, etc. I read a story recently about Bly-ray discs failing because they were supplied in PVC slip covers, which out gassed and damaged the recording surface. But a stack of Verbatim discs without material between the discs, particularly just CDs, shouldn't have that problem, or any other. CD technology is mature enough that they are pretty reliable. Do check who the real manufacturer of the discs is though, as Verbatim did go through a phase of rebranding other manufacturer's discs. They may still be doing that. ImgBurn identifies the manufacturer of the disc, while Nero provides the manufacturer's ID. My current stack of no-name CDs are made by CMC Magnetics Corp.
There is a heap of information on the internet about disc manufacturers and who owns whom, who rebrands what discs, and so on.
I don't know what has caused your problem with the speeds available in MC, but certainly Windows Updates could be responsible, and an update of MC could fix a problem created by Windows Update. I assume that MC uses some Windows components for its disc writing capabilities, rather than write code to do that from scratch. So it could be as simple as a DLL or a COM component change in Windows, or a MC component needing to be re-registered after a Windows Update.
Even a re-installation of the same version of MC may fix the problem, and display all write speeds again.Anyway, no need to change CD burning tool you use. MC does a fine job, and will again once this little hiccup is corrected.