One slight bit of encouragement for your possible black and white
warbler. My only life sighting of this bird was at a roadside rest in
the Owens Valley in California at this time of year. The possibility of
some small numbers of this bird moving north along the E. side of the
mountains on their way to NE British Columbia is plausible. They are
known as rare but regular stragglers to the West coast during migration.

One behavioral item that could help. Black and white warblers can do a
great imitation of brown creepers, moving up and down the main trunk of a
tree. My sighting supported this line from the guidebooks
-Jim Neitzel