Tbh I had the same belief as Agni did but with Gallerian's design and others I realized that in Heartbeat Clocktower they were actually just being potrayed as their representative Vocaloid. You can see that "Margarita" has the collar with a green frill. "Gallerian" has the blue scarf, and "Nemesis" has a collar similar to Gumi.
I believe it's just that characters without a design are just shown as their representative Vocaloid. This is seen as well in Re_Birthday, Clockwork Lullaby, Wordplay, and Full Moon Laboratory.