None of my comment is necessarily earth shattering; however, other nerds may enjoy it.
As many others, I am having some spare time being confined more at home these days. For some odd reason, I figured out the musical key of each song from the "More Hits" album. Here are my results:
All of the songs except for Honey Boy [[Eb) and In Love Again [[Bb) are in the key of C.
Along with all of those songs being somewhat similar sounding [[by HDH), I had often thought there was a certain cohesiveness about them.
I also went back to their three prior singles: Where Did Out Love Go [[key of C), Baby Love [[begins in the key of C); and Come See About Me [[D).

My hypothesis: Those early songs were indeed written to a particular pattern focusing on Diana's sweet spot in the range of notes they would use. The melodies were pretty simplistic.

Although I did not visit many of the post 'More Hits' songs, there did seem to be more of a difference in the musical key in which they were written. Artists are not confined to one key in which all of their songs are sung. It depends on many factors about the melody and the intervals in the song.

I now will go back inside my music nerd land.