It occurred to me this morning that in common usage (and the way the word is taught to little children), the plural of person is people, even though the words persons is used in slightly different contexts, and, to make things more complicated, people can be singular.

Examples:
(a) I almost hit a person who was crossing Empire Avenue today.
(b) I almost hit some people who were crossing Empire Avenue today.
(c) I almost hit some persons who were crossing Empire Avenue today.

I would never use (c). But is it technically correct? (Even if it is, it sure is ugly.)

You do hear in news reports things like:
(d) A person or persons entered the building under cover of darkness and made off with an undisclosed amount of money.
Why this stiff phrasing?

And from government, things like:
(e) We Canadians are a peaceful people.
Which is singular.

What's up with these two words? Why aren't they completely interchangeable?