Italic D: First or second century?

[Gaius Honorius Felix]

The helmet could have been passed down, I dont see why not. So its possible it appeared in the 2nd century. You could take the as an example the B-52 in the US military; It's been in service for 50 years and there is no intention of building more or fazeing them out. So back to my point the helmet could have been used for a long strech. If it works why replace it.