Christies Late Roman helmet: 1 or 2?

[Flavivs Aetivs]

We date the Deir El Medinah to the late 6th century because there's no evidence for helmets of the Leiden Type, the closest to the Dier El Medinah, dating before 580 AD. There's a couple 5th century prototypes from Tarasovo 1764 and another site in Russia which were manufactured in the Sassanid Empire and found in Hunnic burials. They must have been transmitted into the Roman sphere after 450 AD.