To quote you: <<Not to attack Doug's point, which has validity here (that we don't know what factoring advances NSA may have made), but I personally think the combined capabilities of "public domain mathematicians" are now far greater than what NSA has. Shamir, Odzylko, Blum, Micali, Rackoff, Goldwasser, Solovay, Berlenkamp, etc., are top-flight researchers, publishing many papers a year on these topics. It is unlikely that some GS-14 mathematicians at the Fort, not able to publish openly, have made much more progress. I think the resurgence of crypto in the 70s, triggered by public key methods and fueled by complexity theory breakthrough, caused a "sea change" in inside NSA-outside NSA algorithm expertise.
You mention Shamir, etc. However I would point out that even if any of the original RSA mathematicians found a better factoring algorithm, they'd be more than likely to keep it under lock and key. The obvious reason is that their money supply depends on such an algorithm being suppressed. Now, someone outside of their circle with a little less to worry about the impact of such a factoring algirthm would be likely to publish it, but I doubt that PKP's founders would.