Missing form reports

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I recently upgraded my Concrete5 from 5.4.2.1 to the latest 5.6.3.1 This took a few upgrade steps. Unfortunately now I am not able to see some of my previous form results.

I can tell they're still in the database, because I happened to have an old URL that points to them. But when I go to Dashboard -> Reports -> Forms, I only see results from since the upgrade.

Ideas?

Thanks,
Brian