Q. Is it your recommendation to still use a hyphen in a phrases like “mid-1985”? If so, then would it be best to write “mid- to late 1985”?
A. We are still apt to consider mid to be a prefix meaning “middle” in expressions like “mid-1985,” hence the hyphen. The status of prefix means that mid- forms one word in combination, unless it is joined to a capital letter or a numeral, in which case a hyphen is employed: midsentence, midcentury; but mid-July, mid-1985. Your solution of “mid- to late 1985” (short for “mid-1985 to late 1985”) is impeccably logical, though some editors prefer the rather odd “mid-to-late 1985,” because the stray hyphen might be misleading to some readers.
Perhaps life would be simpler if we could just say, following Webster’s, that mid is not a prefix; rather, it is an adjective (sometimes it is an adverb or preposition) of the type seen in expressions like “mid Atlantic,” but it tends toward hyphenated combination form. That would allow us to write “mid-1985,” giving in to the tendency toward combination, and “mid to late 1985,” arguing that without proximity, there’s no attraction.
I would recommend having it both ways, especially if you don’t like either of the “mid to late” solutions involving hyphens. Continue to grant prefix status to mid, allowing words like “midpurgatory,” but when mid strays from its partner, drop the hyphen, allowing “mid to late 1985,” an expression that I think is entirely clear (it’s essentially the equivalent of “middle to late 1985”).