>which send back info on the hashes of the 10 most recent URLs you've visited on the site, IIRC. None of them are unique tracker hashes for a given user, though.
That seems highly unlikely to never be unique for some users.
The hash is keyed and rotates once a day, so it's not a long-term history. And in any case, nobody's trying to build a unique tracker out of it on the other end, which is the main thing (even in our internal analytics, we even throw away the PII we get directly from request attributes after 90 days).