I just received a promotional email about a 3-day companion sale to Europe. Indeed, as a test, buying two SFO-CDG tickets from May 9 - May 19 seems to cost about the same as buying one ticket. It's $1257.16 for one ticket, and $1278.32 for two. When I book a flight for one passenger on united.com, I get fare basis code LKXNC15S. When I book for two passengers, I get the cheaper K2XNC36H.

How does this mechanism work? I didn't see anything in the fare rules for K2XNC36H saying you need to buy at least two tickets. What happens, for example, if I buy two tickets and then split the PNR, or split the PNR and then cancel one of the tickets (within 24 hours)?

I'm not trying to game the system (my travel schedule is already booked during the allowed dates anyway), but I'd like to have a better understanding of how fare rules work. This idea of certain fares only being eligible over multiple ticket numbers runs counter to my previous understanding.

update
https://www.united.com/CMS/en-US/con...uropeSale.aspx