Dressage - lateral work out the gills

We had a most excellent dressage lesson today.  Although I felt like Duke faded quite a bit between our last dressage lesson (Saturday?, with John riding him) and today, John said he was actually pretty round to start.  We worked on lengthening him (or medium trot), and then bringing him back with the magical steady lower leg on instead of on-off-on-off, which works much better (steady leg).  Then, because this is peeling an onion, John added inside bend or inside leg to outside hand connection to make him go very round when he either slowed down or did a down transition.
We did a bunch of 10 meter circles, 20 meter circles, lengthen across the diagonal, and then leg yield.  We did some very very big medium canter (that's how it felt to me) sometimes with a come-back in the middle and sometimes not.
Duke worked SO hard. He got almost as sweaty as when John rode him a few days ago, and was really trying.
Well, not at first.  And John told me afterwards that when he just ignores me, and kind of braces himself, it's ok to be politely firm and say "no, you need to give me your head".  He said it's not ok to rip on him, and it won't work anyway with Duke, but that I get to counterbend and insist that he give it up.  Once he does, of course, I have to give immediately with the reins.
We did some of that, giving with the inside rein when it felt counterintuitive to do it, and Duke would usually get soft and relaxed.  We also did stretchy trot at the end, and Duke was like "thank god" and did an amazing stretchy trot, and then John asked for even more (!), just some leg on and off to really make him step forward.  It blew my mind.
Anyway, Duke was moving great, and we started by talking about the areas I identified where Duke has made some progress just from May to now (notably, not ripping around on the forehand when jumping and requiring a pulley rein in between fences) and John pointed out he's also improved a lot in his counter canter (he used to be very stiff).
It was a great lesson, but one of those frustrating ones because while it's great Duke can move so great, and that I can ride him to make it happen (we even got a series of "yes"s from John!) I don't know why I can't retain it better in my head in between lessons, to work on myself.  It's like it just takes forever for it to stick, and I wish it would stick faster so John didn't have to repeat himself and could spend more time teaching me the next thing, then the next thing, then the next ...