I remember the one where some contractor accidentally cut the trunk between AZes.

In us-east-1? That doesn't sound that impactful, have always heard that us-east-1's network is a ring.

Back before AWS provided transparency into AZ assignments, it was pretty common to use latency measurements to try and infer relative locality and mappings of AZs available to an account.

It was a long time ago. It was very impactful at the time. You could still reach the other AZes but that one. I think this was US-East1c.