Test Collab does support test case versioning.
With this feature any individual update in test case's data is recorded separately as a revision.
User will have option to see all the revisions a test case has been through after it was created, along with the changes done.
If the user's role in project allows him to edit the test case then he can also revert the test case to any of the previous revisions.
The person editing the test case can optionally provide the notes about the revision.
The test case revision number is maintained with the test execution records so that the user who is viewing test execution's details should know the exact version of test case that was executed.
More details on test case versioning are available here.