We also increase tips by going to Guest Services. But we make sure we hand the slips to everyone. We had an issue one cruise where we got the receipts and the names were no where close to the people who were actually serving us in the dining room (sometimes it's hard to tell as a lot of servers adopt "Americanized" names and the slips have their real names). But these were very far off for our server and assistant server (head server was fine). When we went to Guest Services to adjust the tips up, we asked to be sure the tips were going to the right people. We were assured they were; we even had a Guest Services manager confirm all was well (they told us there was a computer mix up associating the wrong names to the wrong accounts or something but behind the scenes, it was going to the right person's account). Something wasn't right and the last night when we handed out the tip slips, we spoke with our server and told him about the names being wrong and what Guest Services said. The last morning at breakfast, our server and assistant server both thanked us for pointing out the issue and giving them the slips. He said if we had just let it go, their money would have gone to the wrong people. But because they had the slips they were able to straighten everything out.
I'm sure 99.9% of the time, all is well. But just in case there is a computer glitch, if having that little piece of paper helps out the people who made my cruise special, I'm going to make sure they have it.