I don't think you're necessarily too far gone...if he's already got the foundation's to the things you've already taught him, it won't be difficult to go back and refocus on them individually, at the same time as you continue refining other things (if that makes sense).
I am constantly overlapping, I think it's safe to say 'most' horse trainers will over overlap some in their training regimine; now, how they go about it will be different; for example, when I teach something, I will go back to that the next time, I work the horse, and then add something new...so I reinforce, while overlapping with a new concept...understand? So what you've done isn't totally 'dumb' or "pointless" you just need to develop a strategy toward picking up where you left off.
Something like this...
You said you always usually work on your come's\stays\disengagings, etc...so use those as your 'reinforcement' cues...things that will be easy for him to do, at any point in your work session; you can begin, or end, or even pick them up in the middle of a session. Then choose a few other things, or just one 'complicated' thing, say lead changes, or your rearing trick, or sidepassing, etc...as the 'meat' of your session; this will be the 'teaching' part of the session.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."