I understand your backwards premise. But it still doesn't make any logical sense. That's not how a business or manufacturering process works. The details are worked out a year or more prior to execution. "LG may give Google priority." Why would any company do that without an incentive? Making panels aren't free or cheap for that matter.
I have a masters in business and a bachelors in communications and your assumptions go totally against how corporations run. This isn't a tv movie. They make contracts for a reason and stick to them. All the legal paperwork have to be signed and stamped well in advance. Then firing up the factory. You're not making money if it's sitting idle.
LG is in Korea and HTC is in Taiwan. They are practically neighbors. The panels arriving in Taiwan would take a little over 2 hours. Even if the panels were produced in China, doesn't take long at all to get them to Taiwan by ship or flight.
The incentive is LG getting the money for building the 2XL. We know LG was contracted to build a third pixel device this year, with the original plan being for two HTC 16:9 devices and a third 18:9 LG model. The bigger HTC got canceled. Part of what factored into Google's decision to go with LG for that third device during the planning phase was certainly the ability to secure a steady supply of 18:9 OLED displays, as was their decision to invest heavily into LG Display. Google also no doubt heard from HTC how difficult it was to secure large supplies of 18:9 displays, which HTC was unable to do for the U11.
You also seem to be unaware of how difficult it is to manufacture OLED displays. Sure, contracts can be signed, but there is ALWAYS going to be some variability in the production rate due to the difficulty in making them. This issue is well known. Besides, if Google planned for 100,000 devices, with an estimated number each month, but they actually sold 150,000, that's 50,000 extra displays that Samsung has to manufacture within the bounds of their contract with Google and anyone else buying their panels. You also have to keep in mind that Samsung usually gives it's own devices priority for panels, and has limited supplies for buyers as a result. (Then you have companies like Apple, which pay billions to ensure that they also have priority for their components too)