By the second half of the 14th century it seems to have been common for medieval tents to have had a rigid internal frame at the shoulder of the tent, circular, polygonal, oval or rectangular as the shape of the tent demanded.
There are several indications when a medieval artist is depicting such a tent, rather than one spread by the tension of guy ropes alone:
No guy ropes shown, (also here) or an insufficient number to give the tent the shape shown.
Guy ropes descending at a steeper angle than the roofline. See also here, here, and here.
Guy ropes meeting the tent somewhere other than the shoulder. Also see here, here, here, here, here, here and here.
Falling tents keeping their roof shape as they fall. Also here, although that one might be being erected.
Realistic depictions of a tent with a smoothly cylindrical valence but folds depicted in the walls.
Dormers on the roof.
There are several advantages to this design. Because the guy ropes can descend at a much steeper angle than the roofline, the tent can have a much smaller footprint. Fewer guy ropes are needed, and less attention needs to be paid to keeping them quite taut. The rigid frame helps the tent shed wind well.
In contrast, Simone Martini's 1328-1330 fresco shows the classic features of a tension-spread tent: guy ropes that descend no steeper than the roof slope (in this case, less steeply,) ropes attached at the shoulder, and a tendency of the roof to sag between the rope attachment points.
But rigid frame tents seem to also have been in use as early as the mid 13th century.
I believe, based on the iconography, that in the late 14th century and in the 15th century this type of tent was more common in Europe than tension only designs.
In addition to the iconography, there is documentary evidence of timber work beneath a valence in 1467 and pavilion hoops in 1511.
Here are more posts on tents.