Whether or not a Zorua sprite is shown with the best buddy ribbon depends on whether the buddy its mimicking is best buddy at the time of encounter, regardless of whether it was best buddy when the spawn was generated.
I noticed this a couple of times during the event, but there's always a chance the spawn just so happen to coincide with the 60 seconds between the buddy getting a ribbon and me swapping to the new one. Video shows a fairly straightforward test – buddy is 1 heart away from BB. I had to wait for Zorua to spawn, which took a truly absurd amount of time. Click on the Zorua, it doesn't have a BB ribbon. Exited the encounter, played with the buddy so it'd get BB. Go back to the Zorua, and now it's got a BB ribbon.
I forgot to show it in the video, but I had two spawns later that were the Bewear and both had the BB ribbon on the overworld, so it seems this applies to both the overworld and the encounter.
It's a curious insight into the mechanism of how Zorua works given that which buddy it mimics is determined at the point when the spawn is generated – so which buddy to mimic and whether the buddy has a BB ribbon seems to be determined at two different points in the process.
by rachycarebear