(Oops! Didn't take time to log in-- MM)
Well, I am now deep in the bowels of
Quirk, et al, Jussive-- and I think there may be some--ahem!-- lack of clarity among everyone, including the texts, between
group nouns and
collective nouns, among other things. Group nouns (according to the book in my lap at the moment) are those you mention as taking
an item of:
a herd of cattle, a gaggle of geese, etc-- where
herd (not
cattle) is the group noun. Here, they list
family and
committee,
for instance, among the group nouns referring to people, with the
comment that there is often a choice whether to use a singular or
plural verb, based on notional concord-- i.e. what the speaker is
thinking.
Meanwhile, in another section (5.78, to be precise), they are comparing
unmarked plural nouns--
people (sing.
person),
police (sing.
policeman/officer),
cattle (sing.
cow?) with
collective nouns, which '
differ from other nouns in taking as pronoun referents either singular it or plural they without change of number in the noun'.
In other words, they are not uncountable, but the singular form can be
in concord with a singular and/or a plural verb, while the plural form
acts normally:
The committee has met and it has rejected the proposal.
The committee have met and they have rejected the proposal.
The committees have met and they have rejected the proposal.
Incidentally, to hark back to the original question,
Quirk lists examples of 'collective proper names':
Parliament, the Vatican, the United States.
That's as far as I am prepared to carry the research tonight-- over to you!
MM