One of the best things about being a guy is that once you find jeans that fit well, you can just order pants based on the numbers - the Levi "model" number, the waist, and inseam length.

Not with Levi's 559s. I have a couple other pairs of "standard" blue denim 559s. They fit great. Then I ordered these grey 559s, same measurements as the other pairs, and they're quite a bit tighter even after wearing them for the usual break-in period. I still wear the other 559s, and they're still a great fit - it's not like my size changed (for once in my life!)