Consider the alphabet (ABC...XYZ). The order is defined, but meaningless.
Say we have a subset of letters: BEKOPX
How can I say that ‘B’ is the “first-est ” and ‘X’ is the “last-est” occurring letter in this given set? Not because of their positions in this set, but because of their positions in the original alphabet.
Consider different-sized photos in an old scrapbook. They have dates on them, but they were not added to the album in strict chronological order. Still, they appear in sequence as you flip through the pages.
"Earliest", "alphabetically earliest", "nearest", "smallest", "least", etc. may work most of the time because there are enough of these words to choose from to avoid confusion when a conflict arises.
The scrapbook example illustrates a few conflicts all at once.