How can I configure a daily, scheduled, *unique* list?

Content

I don't know if I'm trying to do something a little unorthodox, but here goes:

We have incidents to which we assign certain dispositions. We would like to run a scheduled (nightly) export of the contacts to which those incidents belong, to share with a partner in our business.

The problem is that, based on how I've written the query (I'm sure there's a better way to write it) I do not know how to prevent contacts from showing up more than once on a report (not on the same day, but 1 or more days later when the report runs again).