While I haven't played P&C yet (waiting for the full release, heard there was a ton of bugs and a memory leak at some point), it seems like there's a different code for each set of princesses (as well as ending dialog. Neat!). If I had to guess, each code unlocks the 3 costumes for those specific princesses. The dev might have to confirm that though.
Best tip I've got for this is to always have 2 different drinks in your hands. If the table and your hands are full of unwanted stuff grab 2 new ones and hope. Don't be afraid to grab doubles and spill them outright if they're clogging up the counter.
Extra tip: certain princesses getting fully drunk creates a visual debuff. If Moth Princess' full drunk state is any indication, this is intentional. Keep a good eye on what's being placed on the counter and remember what's in your hands.
Good luck! You might need it.