I think there might still be a flight in the 900s that is SFO-JFK-LHR and then another that is LHR-JFK-SFO (or does this work for LAX rather than SFO?). In any case, the 800s seem to be connections (to/from any city to a UA hub/focus city) to Asia/Pacific/South America and the 900s to Europe and vice versa. Hope that helps!

JK-SFO