At least Debian uses a new versioning scheme for xserver (AFAIK it's also done upstream). This means your installers will display something like this:
Can't find the X Server version you are currently running (1.3.0) in
this installers database, so for your convenience, I'll try to install
the driver for the latest available version (7.1.0) onto your system.
Basically, it should be compatible to your Xorg version, so it is safe
to hit <RETURN> here.
You probably want to modify your scripts to take this into account.