[trippypig]

But it was new, it wasn't previously described in print, and it wasn't available to the public...

...oh, before the effective filing date. There's the rub.

But couldn't the case could be made that all of those conditions applied at the time Satoshi released it; and, had the rightful owner known of its existence, would have applied?

I just think the anonymity is really interesting. Why be anonymous? I don't think it's open-source altruism like the mythology suggests. I think it's greed. If he'd developed it for someone else or while working for someone else or on/with (their) prior art, that's a damn good reason to hide. So is (at present) the $6.4 billion USD value of his 980,000 bitcoins.