From version 6, Tinderbox uses the OS's build-in versioning capabilities. Past versions are accessed via the File menu -> Revert To option. Recent versions in the current session may be listed otherwise past version can be accessed via time-Machine-like interface. Note that this does not require the user to be running Time Machine.
The past versions are stored by the OS and are not designed to be readily accessible to the user. Either make use of the 'revert to' option if seeking past versions or use Time Machine if available.
The document autosaves in the background whenever a semantic change occurs. In practice this means that should a (thankfully rare!) crash occur very little recent data is lost. Even unsaved document, if open for a short while, will get saved/recovered after a crash.