Riding Duke after John

Since Duke had his (second) stall rest, I've had a really hard time working him to the right (clockwise).  It is like his neck bends, but his left shoulder isn't moving on the proper track.  John rode him first today - we haven't had a lesson I think since mid-November - and the good news was that I was feeling that correctly, but the bad news was that I wasn't describing it correctly.  John described it as stiff on the left rein - Duke won't give or bend to the left, so he is just blowing off left rein aids.  They got in a little bit of a spat, which John said was when he asked Duke to work harder.  That was interesting too, because maybe that's what was going on with that incident in the indoor arena.
He got quite sweaty from his work with John, but when I got on, he was like a different horse.  He had spring in his step, was light and nimble to the aids, and it was easy to do each aid John told me to do.  The half empty side of this, though, was that while I could follow it (mostly - my reaction time is not as fast as John can talk) - I am not skilled enough yet to ride him step by step.  Which was also a good lesson because I am not even trying to ride step by step at home.  I thought I was, but compared to a lesson, I am just cruising around the arena in cruise control.
He was not off at all with John, though, and I trust John would feel it and let me know, vs the kind of crazy I have been making myself, worrying that I am riding him when he doesn't feel 100%.  Ashley said that thoroughbreds generally don't jump on the day they have their shoes done, that their hoof walls are thinner and more susceptible to a hot nail, and that some even need more than a day off after their shoes are done.
The big takeaways that I can work on at home are - using the outside leg to stop him from moving out (and vice versa, in) on a circle.  If I know that he is about to try to bulge out through his shoulder, I can put the outside leg on at the girth and minimize it.
The other easy takeaway was not pulling steady on the rein, but more of a squeeze/release to move it around.  It is not always a pull back - sometimes it is just jiggling it in Duke's mouth.
We did 20 meter circles, then 10 meter circles, at the trot and canter.  I could feel that he was better balanced - his shoulders felt more square and even.  John had me use my leg with the steps (now-now-now-now) and then, when Duke wanted to rush, slow my posting to slow him down.  He also reminded me at the canter to sit down, not to tilt forward like I am prone to do.
Both legs and the outside rein were a half halt, to balance him.
I kept contact with the outside rein so he had somewhere to reach to, and mostly used the inside rein.
If we were on a circle, and he was bulging his shoulder out, the first aid was a half halt with the outside rein.  If that didn't work, then counterbend to the outside.  As soon as he gave, bend (slowly) back to the inside.
I think John can see the shoulder about to pop, so he has me start giving aids just before it happens, to try to prevent it.  I don't always feel that it is about to happen though.
It was one of those lessons that was great, in that John figured out what my issue was, then told me how to fix it, and I could feel the difference after John's aids, how much better Duke could move.  But it was also a lesson where I realized just how much I still don't know and how much there is to learn. With a few weeks without riding or lessons, I feel like I regress years backwards, and it is frustrating - by 41 I'd like to be a little more confident that I know what I'm doing.