The head pattern you described does fit RBNuthatch rather well, if we start from the premiss that you are very familiar with Eurasian Nuthatch as I am, I’ve been watching the latter at point blank range (6’) almost on a daily basis over the last 30 odd years (generations of Nuthatches), and never once encountered an aberrant bird!
Most years I visit the US and not infrequently encounter RBNuthatch (although certainly not always), to my eye the head pattern always reminds me of a Cavalry officer’s “dress” trouser ie the white supercilious being quite stark and contrasty.
Well that’s my tuppence worth....let’s all hope it returns.
Thanks Ken. 'stark and contrasty' is a good description. Yes, indeed, let's hope it returns. As always I have the binoculars and camera at the ready.