There's a catch i'm afraid to my Great Courses subscription

I tried over and over just now to play a lecture that I must have let play while I snoozed, and because it shows that I already listened to it, it keeps going to the next one, thus seemingly necessitating a purchase of the course if one wants to re-listen to anything.

If I find a way around this, I'd be overjoyed, but i will not be purchasing any course unless I live off of every phrase the professor speaks.