The age of the JPA archive is not an issue. I just tried extracting a backup taken from our site in 2012 on Joomla! 1.7. Just for kicks I tried several other backup archives taken in 2017, 2016 and 2015 on our and other sites (including my blog), single- and multipart. I tried an even older backup taken with Akeeba Backup 3.2. That's important for me because there was a slight change in the JPA format between 3.2 and 3.3. I finally tried extracting a backup taken with JoomlaPack 2.1 on Joomla! 1.0 back in 2009. In all cases the backup extracts successfully.
Is it possible that you were missing a backup archive part or the permissions of the folder or the backup archive itself didn't allow the application to read it? I can't see any other reason why that would happen.
Nicholas K. Dionysopoulos
Lead Developer and Director
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