I do not doubt that this is correct however if you issue a ticket on 016 ticket stock and it incorporates UA's Contract of Carriage, what triggers application of the operating carriers Contract of Carriage where such fees are mentioned?....
Please see
UA Contract of Carriage Tariff Application: Section A) 2nd paragraph
"Where a passenger's ticket indicates UA will provide the air transportation, but another carrier will operate the flight pursuant to a codeshare arrangement with UA, the terms and conditions UA applies will vary from those set forth below, and vary depending on which carrier operates the specific codeshare flight on which you are traveling................."