Do we need the p() for anything other than [Date]? All the other fields should have a direct effect on what values of [Date] are possible, and so I think selections in them would indirectly count. I may be missing something but it seems to be working on a simple example I'm fiddling with. So might this do the trick?
Wait, since other selections affect what is possible, neither approach works. I think we have to explicitly tell it which fields to ignore, not which ones to use. So... dollar sign expansion with a funky concat(). Hmmm... something like this, assuming all these fields are on a calendar connected only by Date to the rest of the model?