Great question Kvalois!
1967 was a transition year for Glen and guitars. Early in 67, we see him with a Mosrite Balladere
in a lot of media and we know he was pictured with his Martin
during that time. Glen used the Mosrite early on in the Smothers Brothers replacement show...but dumped it as soon as he got his Ovation, which would have been mid to late 67.
So, depending on when Gentle on my Mind and By the Time I Get to Phoenix (we see the Martin exclusively in the photoshoot for Phoenix) were recorded, he may have used an Ovation, but he may have used the Martin.
In '68, I am guessing he was exclusively using Ovation in the recording studio.
Either a Balladeer or once Charlie put the Glen Campbell Deluxe Balladeer
in his hands, he would have used that.
I would speculate that on Wichita Lineman, or any other record recorded in 68, it was nothing but Ovation.
There are others lurking here, that have forgotten more than I know about Glen and his guitars. Maybe they will chime in.