Check the Gallery for hints at each ending! :)
I already got every ending though, that's the thing. The ending came before I was able to deliver the final round, but it was still the 'good ending'. I just don't know how to delay the ending by a round.
(The game also doesn't tell you how to get endings if you've already gotten them, so I can't use the 'spoilers' option double-check the trigger conditions and intentionally avoid them somehow)
Nevermind, I decided to look in the code for it. It seems like maybe it was a planned ending that didn't get finished, or maybe it's just supposed to be a red herring? But despite Peaches asking for 10 milk and Nessie asking for 15 (and Brooke only asking for a regular 5, lol), there doesn't seem like anyway to deliver it and see their size afterward. 😔