This is here mostly for my own future reference.
This is a fresco from the Schifanoia Palace in Ferrara, painted from 1476-1484. In the center is a man wearing an unbelted giornea, with the fabric falling in natural folds. On the left is a man wearing a giornea with the small tubular pleats that are typical of the style. This indicates to me that this depiction of pleats is not just artistic license, but an accurate portrayal of the style.
ETA:
This painting (Botticelli, 1483) also shows different styles of giornea. The man in the foreground, the man in the center with his hand raised, and the man on the right all seem to have giorneas with natural folds, while the man in red (right next to the horse's nose) has rigid pleats that start at mid-chest. Looking at the form of outer garments at the end of the century, I would guess that the rigid pleats are going out of style at this point and are being replaced with more unstructured garments. Either way, this bodes well for future Pennsic wardrobes. :)