Glenn Gould was said to sometimes analyze and completely memorize works from the sheet music alone before playing them at the piano. His father recalled an instance of him learning an entire concerto from the score alone and then playing it from memory the first time, and Bruno Monsaingeon saw him play an entire movement from memory of a Mendelssohn string quartet after hearing it once on the radio (quoted in Bazzana's book on Gould).

That pales in comparison though to the fourteen-year-old Mozart transcribing from memory after once hearing the secret Miserere of Allegri, a dense polyphonic work that was performed only in the Sistine Chapel and was forbidden by the Vatican to be transcribed or reproduced under penalty of excommunication.

I sometimes found piles of sheet music sitting around in my high school's music room, and I'd read them once in a while.

I'm by no means an expert at the piano, but I'm probably halfway there, and I can without too much trouble get the general gist of complex unfamiliar piano music, and I can easily read simple music. I'd say it's pretty much analogous to the ability of expert chess players to play blindfolded, which is definitely a well-attested ability. (The record for simultaneous blindfold matches is around 50, played by Janos Flesch in Budapest in 1960.)