it will maybe be possible to open the ttx (based on inx) file which was created on a higher Trados version, but in most times you will have problems to save the ttx back to inx.
The rule is more generic - problems with saving TTX back to INX appear in about 50% of the projects. No matter what version of Trados was used. Move the TTX to the reviewer/QA/other computer and you won't be able to convert it back.
And because your old Trados version has problems to recognize the newer tag structure in the ttx file you will have some bad segments in the memory, so that you have to adapt the translation again.
Once the file is converted to TTX, the version of Trados/TagEditor is not that important (if you don't insert new tags using toolbars). You only have to fix the headers in TTX file to be able to convert back (usually PluginInfo goes bananas).