How many can be "first" or "last?" [closed]

Solution 1:

My thinking and my dictionary say there can be only one item or event in "first" or "last" place

There can be more than one "first" or "last" thing. You've already given two examples yourself ("first five", "last group", and ties). This concept is applicable in more contexts, not only in the exact kinds of phrases that you gave. As Jason Bassford said in a comment, the number is assumed rather than stated in other phrases; for example, "the first few minutes of an exam" (Cambridge Dictionary) or "the first responses to my question came yesterday".

The expressions "one of the first" and "one of the last" are simply combinations of the "one of the" structure with the uses of first and last to refer to groups or collections of items.

The meaning of a word isn't derived from its dictionary definition, but Cambridge's definition A1 does fit pretty well with this use of first: it is "coming before all others in order, time, amount, quality, or importance". When you consider a group, "all others" generally does not refer to other members of the group; rather, what it means to say that the members of the group are "first" in something is that they come before anything or anyone not in the group.