Well, the only reason you can directly skip from 9.8 or below (ish*) to 9.10 is because 9.8 and below did not enforce the support entitlement at all. It seems like Ruckus has always wanted you to keep an active support entitlement on a ZD, it's just never been enforced by the software until 9.9. That is the "important restriction".
(*) I say "ish" because there actually are some upgrade paths where the image format for updates have changed and you cannot directly jump. For example, IIRC you cannot directly go from 9.5 to 9.8+, the image file just won't get recognized by the older firmware. For some unsupported jumps, Ruckus will just force you to go back to factory defaults. The release notes always explain the officially supported migration paths. Some of the unsupported paths do seem to work with caveats, but you're probably on your own to do that.
