I would say go with this approach on a sandbox first and test resolove all issues:
Side-by-side:
New installation of 8.2 version and slowly migrate components from 7.1.2 to 8.2
If you have any time constraints like sooner upgrade then you can go with “Over Install” approach (caution) – And yes your definition/assumption is correct:
Yes, direct migration from 712 to 822 is not supported. But this should only be followed when you need to move you data from 712 (like bpm runtime etc). if data is not required then packages can simply be exported to 8.2 … this too is supported by SAG