a pseudo Black-chinned excuse for ISO 8000

A female ruby-throat type hummingbird appeared in southern Berrien this week.  Given that ruby-throats are pretty much done migrating (I don't think I've had one at my feeder in at least a few, perhaps several, weeks), the possibility of a lost Black-chinned was raised.  It was dark and rainy and I was pushing the ISO up much higher than I ever really have before; the pics turned out fairly well all things considering.

So, who's been giving legitimate actual study to the Ruby-throats at their feeder?  I know I ... (hmm, awkward pause) ...  definitely have not.  Sibley says that ruby-throat has much more contrast to the face, his illustration has the ear blending more with the throat in Black-chinned.  I think the above pics are representative of the bill length.

Here's a comparison female Black-chinned from Arizona showing its blended face and longer bill.

 
A character that I guess I should study more is the color of the forehead and cap.  Pyle says that Black-chinned lacks green tones; its cap is brownish or gray.  Honestly I don't see a lot of green here so clearly I should look at more young hummingbirds next fall.

One of my pics early on seemed to suggest a purplish gorget feather which would be very strong support for Black-chinned.

I tried really hard to get an unequivocal shot of a purple feather there.  This was as close as I could come and it would seem that it's more likely an artifact of some feathers out of place.

I don't honestly own a specialty hummingbird guide.  Allen Chartier said that a young Black-chinned should have buff edged primary coverts which this bird clearly does not (apologies if I over-simplified, if so blame me, not him)

A view of the only shot I lucked into of the spreadtail.

If a person knows what they're doing the shape of the outermost primary likely cinches this as a Ruby-throat.  Unfortunately I have far more frozen wings of Costa Rican Hummingbirds than I do of the one in my backyard...