Did spaulders/pauldron ever not use sliding rivets?

[Buster]

I'm asking because I've noticed at least one 14th century effigy showing what looks to be sliding rivets on the spaulders.
http://effigiesandbrasses.com/monuments ... 349/large/
Is there any reason to think 14th century spaulders didn't use sliding rivets?
(They seem pretty necessary for stabilizing the piece.)