How To.. wear the Pugio and Gladius (belts, fasteners)

[Tarbicus]

But it seems as
if only part of a belt was found UNLESS some belts of that period only had
five plates OR plates were missing from the belt before deposit.

This is something you have to be careful about. There is a very learned opinion out there that a military belt wasn't always jam-packed with plates, with many only having about five plates in total.

The button fastener illustrated in Miks could also keep the gladius to the armpit if the top holes fed the strap above and over the belt, with the bottom holes feeding a strap below it. Not much difference to the single criss-cross strap secured with a buckle really.