My eyes must be playing tricks. I assumed Zoser's coin was silver from the photos. But clearly it is bronze as you have pointed out.
SNG Cop. definitely lists the
triobol as a silver coin (AR).
From the links you provided 3 separate dealers reference it as
SNG Cop. 364 despite their coins also being bronze. I would have thought the convention would be to use
cf. if it is a similar coin but different
denomination.
So I am at a loss. Perhaps someone else could clarify.
Peter