I think you might be right, I've seen some where he's looking at the prompters nearly the entire way through and I remember one at a rally (I think in Wisconsin) where he went off-script early and stayed off script for so long he even joked something like that the teleprompter operator probably wonders if they should just take the rest of the night off.

In this one he went off-script a lot for the second half and seemed to only look at them to check the time or for bits that are harder to remember like anything with exact numbers and times while improvising everything in between.