Thanks for your reply, very useful info. What's the difference between "end on end" and a side trip? It looks like side trips are allowed but end on end is not allowed.

I guess "end on end not permitted" means that I cannot book any roundtrip ticket on United departing from EWR during the days of my HKG-EWR reservation? What if I was staying in EQR for 6 months? I wouldn't be allowed to take another roundtrip from EQR at any point in those 6 months? Or only if such trips would result in a lower total fare? Is there specific definitions of end on end and side trips as defined by United?

Would I still be breaking the rules under the following scenarios?

1. EWR-SDQ on another airline
2. JFK-SDQ on United
3. EWR-SDQ and SDQ-EWR booked as one way bookings on United.
4. Staying a few days in EWR before going on to SDQ