15thc perception on swallowtail merlons?

[Pierre Dumont Himself]

Yes, I'm fairly certain they wouldn't be depicted if they hadn't been there. The seal was made by the Count of Gorizia, who clearly knew what it looked like. His main residence, Schloss Bruck bei Lienz, never had swallowtail merlons.

 Interestingly enough, they were still included in the 17th century reconstruction, after the castle had been razed and rebuilt, but disappeared at some point in the 18th century. 

Of course, it should also be included in the "Non-Manuscript Art" layer.
Edit: You can also compare it to the Seal of Trieste: