Hi Zarabatana. I just added a set of IMDL files to the Letter-sized version of the template that should work with older versions of InDesign, but Creative Cloud won't let me install an older version of InDesign to actually test it and be sure it works correctly.
Is there any chance you could give it a test and let me know if it works? I would really appreciate it!
If it works, I'll do the same for the A4 version of the template as well.
Look for the folder InDesign Template (Compatibility Version) (it's in the InDesign Template folder) for the IDML files and instructions.