On your personal computer, if two applications differ only in their version numbers, then the last copy installed is the one that gets launched. However, this rule doesn't apply to applications on an AppleShare volume.
A sure way to eliminate the version (or last-installed) confusion is to change the Creator of the applications you don't want to launch.
For example, use ResEdit to change the Creator of HyperCard from "WILD" to "FRED". When you double-click on a stack, the system looks for the application whose creator matches the creator of the document or stack. If you have another copy of HyperCard (say, 2.0v2) on a mounted device, it will be launched. Saving files from the changed application is unaffected (they still have "WILD" for their creator).
Change the creator of all non-current HyperCard applications to something other than "WILD" (try "DLIW"; it's probably not used by other applications). All stacks launched will come up in HyperCard 2.0v2. To open the stacks in other versions, launch the desired application and use "Open╔" in the file menu.