Re: Opening tunes written version 1.75 with version 1.70
...unless they all upgrade to version 1.75 which isn't an option just now.
While you haven't given the reason that upgrading is not currently an option, with the very greatest of respect, $15 US to upgrade to V2.1 is almost nothing ($25 if you want the CD as well) and the appearance and features available are considerably improved over all previous versions. I strongly encourage upgrades over messing around.
https://www.noteworthysoftware.com/order/wizard.php?formid=nwc2u