All characters who supposedly have a first name must have a source to prove their first name.

Someone might hear from a friend that their friend heard that MacGregor's name is Oliver, and thus assumes that it must be right. He must have a first name, right?

Wrong. Many important characters don't have specified first names. That's just the way it is. Unless their name is said in-game, like when Braeburn says "You know what Donnie, why don't you just-", or there is a reliable source stating their name, like how Roland Roger's name is only said in the special edition of Big Red One, their name is not to be listed. Soap's real name wasn't known until Robert Bowling disclosed it on Twitter.