This doesn't sound like a JFK CSR issue (given that he had the same problem with HPN CSR). JFK is a rather small station without that many flights per day (but on the upside, it's possible to know a chunk of the agents there without being GS). The last UA flight arrives around midnight, so there's a few UA employees around for that (around baggage, if pre-security), but otherwise, things thin out a lot after the last flight to LAX leaves.