"I am a program manager at Microsoft.
I'd like to point out that the link Spacedog has posted is what you should go by.
I think the confusion exists because there are essentially two part of a DirectX SDK download.
1) The runtime, which is a redistributable that game developers redist along with games
2) Libs, Samples docs etc. that game developers use to build their games.
Since 2003, the runtime/redist has been frozen at DX9.0c. The runtime has not changed since then. Period.
However, there have been SDK updates every 2-3 months that package up the frozen DX9.0c runtime and updates the libs and samples etc. These are what have versions of the form DirectX 9.0c (date).
If there are any additional questions, please send mail to email@example.com"