Apparently, the Intercisa is several decades after Palmyra, so it could be ruled out. Nor is it a closure. Intercisa appears as a response to the economic collapse of the Roman state and the adoption of new manufacturing techniques. https://imperiumromanum.pl/en/curiosities/fabricae-roman-armory/ Intercisa is definitely out. It is due more to the financial collapse of Diocletian's time.    Forging a spherical bowl in a single piece required highly skilled artisans and many hours of work. • In contrast, the Intercisa design allowed less experienced workers to cut prefabricated iron sheets, join them with a central riveted band, and assemble a functional helmet in a fraction of the time. "With the third century A.D. and the growing threats at the borders, the design of Roman helmets evolved towards simplicity, pragmatism and low cost of production. The steppe and Sassanid Persian influences began to be noticeable, especially with the reorganization of the army and the appearance of government armor factories". Regarding Eastern archers:  The lighter archer levies, or those raised in emergencies, used caps of pressed felt or hardened leather.[[Here I will need a source to validate this] The movement of the bow: When drawing an Eastern composite bow, the string is pulled back brushing against the cheek or the ear. If the archer were wearing the enormous metal cheek-pieces of a Roman legionary, the string would constantly strike against the helmet, deflecting the arrow and ruining the shot. Some helmets with this description would definitely be ruled out.   https://www.romanarmytalk.com/rat/showthread.php?tid=17085  

For champion infantry.

What I have found in my research. At this stage the Romans discarded helmets of Celtic origin or of that style of manufacture. The Neiderbieber style was the last to use the evolution of the imperial gallic coolus as a base. https://www.ospreypublishing.com/uk/osprey-blog/2025/roman-infantry-helmets/ Both Montefortino and Coolus are called "Jockey cap" helmets  H. Russell Robinson. Despite this, the Niederbieber is the only helmet that the Romans created themselves. It was neither Celtic, nor Greek, nor Eastern. The source says that: "Throughout their development, Roman infantry helmets had one thing in common: the fact that their origins always lay with the equipment of peoples Rome had encountered on the battlefield and subsequently adopted (and adapted). The Montefortino, Coolus and Weisenau/Imperial-Gallic and -Italic helmets were all derived from helmets of the inhabitants of north-western Europe. By contrast, the Late Roman ridge type helmets were adopted from steppe prototypes to the east, which appealed because their composite construction was less troublesome than the earlier one-piece bowl examples. Arguably, the only true Roman development was the Niederbieber type, with their deep neck guards and close-fitting, large cheek pieces, and these were only a natural progression from Early Principate helmets". Apparently, the type of manufacturing is what differentiates each model or type. I will try to read the entire source, that is, the book: Roman Infantry Helmets by M.C. Bishop.

Sure. My Gitea account is @bowen951209. By the way, do you mean it's currently not possible to sync with CI like what I said in the first solution?

That's because 1) Gitea is lacking some features and 2) due to defacing issues, I need to grant you permissions. then you'll be able to edit it  Do you want some ? What's your gitea account ?