or they didn't think about the problem of how much public domain literature there is that overflows even negative unix int64 timestamps - it's 1970-2140 for 64 bits - 2037 for 32 bits, so i think if you allow negative ones to mean before UNIX epoch then it couldn't be more than 1800 before it flips to ~2140
Discussion
nah, in fact, relays can and do reject events with funny timestamps, certainly, auth timestamps "should be" constrained to a short window of a minute or less in order to stop replay attacks