15thc perception on swallowtail merlons?

[Mark Knowles]

It is easy to find buildings with swallowtail merlons, but hard to establish whether they had them before 1450. If we disregard the date, we might as well include the Kremlin walls, but doing so would muddy the waters and dramatically reduce the informative value of the map.

Clearly we shouldn't disregard the date. But there is a difference between those that we know post date 1450 and those whose date we don't know.