If you're buying a new MAC, the older versions of the software just flat out will not work on the newer version OS. What you need to do is open the old tax returns and them save them in PDF format. Then burn the PDF's to CD for posterity. Now when you elect to save as PDF, you want to elect to save everything, which will include all worksheets and calculation forms. Not just the forms "for your records" and not just the ones "for filing". You want absoutely everything saved to PDF.
Now for versions of the program for 2014 and earlier, there is flat out no way to get the required updates and corrections. But for 2015 and earlier you can download the latest update for each tax year (2015-2018) at https://ttlc.intuit.com/community/updating/help/manually-update-turbotax-for-windows-software-basic-... and burn that update to CD to store with your CD copies of TTX 2015 thru 2018. No guarantee though that you'll be able to install those older versions on the newest version of MAC's OS though.
