If you have a Travelcard season, unresolved journeys don't matter (as
long as the endpoint is within your zones). And PAYG isn't valid on
National Rail between Ealing Broadway and Paddington.

How would it "know" that the endpoint was in my valid travelcard zones
(1-3 incidentally - I have some PAYG credit as well)?

I could just as easily gone to a tube destination in zone 5 and failed
to touch out; isn't catching that possibility the point of the £4
charge?