No specific “aircraft exit dates” were specified in the document as they didn’t have the delivery dates nailed down.
In the "Ninth Amendment" of that CPA, dated July 2018, it gives a range of exit dates starting from June of this year to August 2020. Also, this CPA is just for the 175s, and does not include 20 CRJ-700s Mesa also has expiring starting this month. So in total, there are 50 UAX planes in the 70-76 seat range expiring over the next year.
My guess is that UA is going month-to-month on the expiring planes until a final final decision and announcement are made.