Most of the rolls were just badly stored, but one of those rolls, it turns out, was already mostly exposed. A wildly-expired roll of Kirkland Signature 200, someone shot some photos of a parade and a eastern-California road trip on it, rewound the roll back into the canister (leaving just the lead out which is exactly how a new roll of unexposed film looks), and left it in a garage for a decade.
I'm guessing the photos were taken by the friend's father, and probably with one of the Leicas in the box with the film, but I'm making assumptions here. I really know nothing certain about the first exposures on this roll. My shots were taken in Modesto, completely with no idea that I was double-exposing.