I had e+ access for 1 year. Bought in April, ran out 1 yr later.
The website then said that if tickets were purchased while e+, would be valid for upgrade and I chose my e+ seats.
14 months later, DEN-KOA, the e+ ran out and we were in e- in the middle after a sweep, but the return was in e+ and was not disturbed.
YMMV. I suspect the change was due to an equipment change, but can't prove it.