It could also be that Stevie would've made an album with the band if Christine had not come back.
After the 2013 tour, say Stevie does her thing in 14. Comes back to Mac to record in 15 and tour with Mac in 16.
I remember when she was doing Unleashed press she said just this one tour we're only doing songs you want to hear and the next time we tour we'll be playing a new album
I mean the SYW through EP years must've meant something to her. Those Say Goodbye Vegas 2013 tears were coming down like rain!