classifiers and plural marking

[Frans Plank]

Concerning David's "corrections" of Alan's "inaccuracy":

On the evidence of agreement, game plurals in English are plurals, using
the zero allomorph for that number, exactly like a few non-game plurals
such as THESE SHEEP, POLICEMEN, HOVERCRAFT ARE ..., and perhaps nationality
words such as THOSE SWISS/JAPANESE WERE ... (assuming these aren't immune
to Number being adjectives, sort of).  Number is *obligatorily* marked,
then.

I don't understand why David includes FURNITURE (a non-animate collective
non-count noun, itself singular and, unlike animate collectives such as
POLICE, requiring singular agreement) in his list.  What is FURNITURE to do
with optional number marking?

Frans