Of course they only call her Ada...You only call those you respect by their last name...Well, Leon was very casual with Ada, hence the reason he only calls her that...Krauser calls her Ada because he works with her, and calling her just "Wong" would show some sort of animosity, which granted, he had, but he wouldn't let that compromise the mission, and Wesker was her boss...Plus...As a spy, she can't have her last name, even a fake one, known too much...I'm glad you can try to back up your arguments, but how often do you call people by their last name only....Even when being called Mr. Kennedy or Mr. Redfield in the games there is still that "Mr" in front of it...So surely if someone were to call Ada by her last name it wouldn't be just "Wong"...Besides, Ada kind of plays by her own rules, and think how few people ACTUALLY know her as Ada...Most people are either dead before they find out, or they are like Leon and she straight up tells them cause she trusts them or is using them in a way which will pretty much end in their death...I just don't understand why you say it's basic for them to use the last name, because that, in my experience, is very rare unless they are using it as a sign of respect...