1912 Publication of a La Tène Shield

[Crispianus]

Part 3 has a translation of the original description of the shields from La Tène and how the thickness varies from centre to edge  I will add a picture when I have time and energy.

" The shields have a short horizontal handgrip reinforced with iron instead of a long vertical handgrip like Viking shields."

In your article you mention a difference in the orientatation of the handgrip, this is not actually the case in terms of construction.
All grips to my knowledge run in the same orientation to the planks as earlier shields, and all appear to have the same inset handgrips with the exception of Gokstad, some with extentions which you might consider as a reinforcement across the plank construction.

This I believe to be true for all early medieval round shields the main difference is in the use oval/oblong vs round shields, Early Anglo Saxon, Frankish, Merovingian, Scandinavian Vendel, Valsgarde or Viking Era.

The Gokstad shields appear to have been reinforced by the museum with additional strips of wood across the planks in addition to the central original, and the suspicion is that they were purely votive hence there was no effort to inset the grips, one side of the ship had yellow the other black/blue? painted shields... Night and day Crew?
I made several of these shields and they don't handle well because of the raised grip, an inset grip is better balanced.

Gokstad with edging and a cover added likely better then the original, made from commercially available spruce.

           

Even the Roman scutum from Dura is in the same orientation, if you consider the center layer of the three ply construction as this runs vertical to the horizontal grip.

There is the Doncaster shield but think the interpretation of the remains may be at fault, as my thoughts are its a large round shield similar to the illerup finds, though I'd have to look closer at it.