Intercisa helmets - photos

[Medicus matt]

it would be logical to infer it was made of a material that could not have survived under the circumstances it was found in. E.g. Wood, horsehair, feather, etc

It would be equally logical to summise that they were simply deposited without their crests. Even if the crest itself were made from a material which had perished, the supporting mount which engaged with the helmet itself would have been metal and would have left some trace of itself.