Check with Adobe. They always offer an upgrade price of some sort (even though you actually get the entire program -- but at a discount). In addition, when one version is purchased so close to the release of the new, they've often made special allowances.
But you should check with them to find out.
I found a form to submit a Post-Announce Upgrade. Hopefully that works.
I found a form to submit a Post-Announce Upgrade.
That should work fine. Adobe has always been very good with purchases within a certain period prior to release of a new version. I cannot imagine that they would change that policy.
If you registered you PrE 7, you might also get an e-mail on the offer to upgrade to PrE 8.