I wouldn't use that as a guide myself but I get your point totally. We got an Eastern wood-pewee earlier this year and that was a first ever. I am apparently the 2nd person here seeing this particular swift (same location 2 weeks after the first sighting) but Martyn (Kenefick) hasn't made a conclusive opinion so far to my knowledge on it's ID. I guess I might file it under possible Chapman's/Chimney /Vaux swift for now.Chimney Swift was not on the T&T bird list per 2007 and is not included in the Field guide by Kennefick et al. So with a single image of a bird explainable with a local species I would go with that (Chapman's).
Niels