You are right in all the technicalities, Jeff. And when I say that the volume day is not linked to the intensity day I only mean they are not linked from a linear progressive standpoint. In other words, you do not use the volume day to "predict" the PR day. Intstead the PR day in some sense predicts the next PR day.
Yes, one PR does not lead to another...for the most part.
Interesting. I understand that a PR attempt is simply an expression of your current preparedness (fitness - fatigue), but if the volume day drops off then the PR day should drop as well, unless you'd been working with some accumulated fatigue. If fatigue is present, then PR's can continue as fatigue dissipates. If not, then the reduced volume won't be enough stress to improve/retain fitness and it'll drop. At least that's how I understand it as of now. You know this stuff better than I do so what am I missing?
You're getting highly technical with the fitness and preparedness stuff
I just said fitness because it was a general term that most people would have some idea of. But you're right about preparedness so let me give a highly techinical explanation of all this.
Training stumulus gives rise to two things: fitness and fatigue.
So the 'fitness' is the postive affect of the training stimulus. The fatigue is the negative affect. The presense of fatigue 'masks' the presence of fitness. PREPAREDNESS is simply the summation of the afteraffects of those...basically the difference between them or what is left to work with given the two different effects.
In a way, you've answered you're on question except to misunderstand what a back off is. A backoff is never done to the point that it allows you to "lose" fitness. Only to the point that it allows accumulated fatigue to drop enough so that the gains in fitness that are occuring as you recover can be shown...i.e. greater "preparedness".
I think you may be overestimating what it takes to allow this. The idea is just to reestablish progress not to actually drop in maximal ability. That is not going to predict what will happen on PR days but only that PR attempts should be continued. At any one time on the program just go for a single heavy set on PR day.
This part is the most important:
If not, then the reduced volume won't be enough stress to improve/retain fitness and it'll drop.
There is a huge difference between the stress required to improve fitness and that required to maintain it. This is really fundamental stuff when if comes to strength. But without getting into different kinds of strength and all that let me point out that we would be in big trouble if we always had to maintain the same volume in order to retain strength! Sure, sometimes you may take two steps forward one step back but that is not always the way. It is quite possible to take one step forward, rest, take another step forward....etc, so on.
But in terms of absolute strength as long as intensity doesn't drop with much less volume than it took to get them. How much and how often is up to the individual and their level of advancement.
You understand this better than most but in your quest for perfection I think you may be overcomplicating it