CSDVersion key for Service Pack

I was looking up the changes in SP3 and SP3a, and basically the ways to
identify the service pack is installed on the system. In one of the
references I found that the CSDVersion key under
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer\ MSSQLServer\CurrentVersion
has changed.
I wanted to know whether the CSDVersion key changes with every service pack
release.
From what I have heard, that is not a reliable measure.
"Harshal" <Harshal@.discussions.microsoft.com> wrote in message
news:AAE3B70A-AEDE-4350-B872-D44697DD759F@.microsoft.com...
> I was looking up the changes in SP3 and SP3a, and basically the ways to
> identify the service pack is installed on the system. In one of the
> references I found that the CSDVersion key under
> HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer\ MSSQLServer\CurrentVersion
> has changed.
> I wanted to know whether the CSDVersion key changes with every service
> pack
> release.