I think the definition would have to be a little grown up in accepting realistic caveats.
Certainly for most hardware that is working from a given kernel version you can reasonably expect it to continue working until the hardware is becoming a museum piece. In the cases that don't you know it worked for at least one version of the kernel and if you care enough (or pay someone to care) you could get it working again. This is a mark about freedom of hardware not assurance of eternal support.