A plpgsql function that turns a user-supplied epoch timestamp (string or JSON number) into timestamptz and promises to raise only check_violation (23514) can still fail with other SQLSTATEs. A guard like abs(n) >= 1e15 is not enough: negative values between about -2.1e14 and -1e15 ms come before 4713 BC, where timestamptz stops, and raise 22008 "timestamp out of range". Digit strings longer than 131072 characters make text::numeric raise 22003 "value overflows numeric format". Postgres also accepts '24:00' and ':60' in timestamp input, so pg_input_is_valid by itself is not a strict ISO 8601 check.