Wow, this is a walk down Memory Lane!
United's Royal Pacific Service predates UA's purchase of the Pan Am routes. UA launched SEA-HKG/NRT and I believe GMP and the moniker for these new routes was Royal Pacific Service.
In 1982 or 1983 when Pan Am was still around in its original form I flew UA for the first time from HKG-SEA-DEN-BWI. I wanted to try it. Customs in SEA was so bad everyone missed their connections. The agents walked up and down the lines at Customs reminding everyone it was not too late to fill out their forms completely but once they got to the agents they would be done for. And it worked, many people were scribbling away on their forms as I recall.
It was very memorable for me, having only flown SQ SFO-HNL-HKG before. (Did you notice none of these routings are around any longer on UA or SQ with the exception of SEA-NRT?) And after missing my connection I was rerouted SEA-ORD-BWI and on the last leg got to fly on a brand new 757, just days in UA's fleet. We marveled at the overhead screens staggered down the length of the aisle and the size of the engines.
I don't clearly remember if UA kept the Royal Pacific Service name for very long after the purchase of Pan Am's Pacific division but I can tell you it started before then, when UA finally got route authority for Hong Kong, Tokyo and Seoul.