Thanks for pointing out the song listing with corresponding notes on "The Vocal Range Of Stevie Nicks." It's a big help, and was hidden on my screen (I missed the "Show More" button to bring it up – my apologies).
I am dividing the list of Stevie's falsetto performances into three sections: studio, live, and demos/home recordings. For whatever reason, she sings a lot more falsetto on demos than on other performances and recordings.
Here's what I've found: Going back to the '60's and Fritz, she doesn't sing a ton of falsetto, as she has a husky voice, but she does sing it regularly. As time goes on, and especially when she starts smoking (
1977?), she starts to use it less and less (and increasingly just for backing vocals or on wordless "oohs"). On the 1975-76 performances of "Over My Head" she nails the falsetto perfectly, but on Japan 1977 she can't quite sustain it and her voice breaks halfway through.
In 1981 she pauses her singing as the background singers do the falsetto on "Dreams." Same in '82 with Lindsey and Christine doing the falsetto as Stevie pauses her singing. She discontinues falsetto altogether after 1982-83.
Around 1998 and "Sorcerer"–about a year after she quits smoking–she resumes using falsetto, but only on occasion and
only in the studio, never live. Perhaps by then studio technology had advanced to the point where fixes can be made that could not have been made 15 years prior.
If anyone has an example that contradicts or adds to the above, please let me know.
I am still reviewing material, and when I'm done I will post three lists (live, studio, demo) of all the falsetto I've found. It won't be complete, as there are just too many demos to go through, but it will be extensive.
Finally, I'm not sure that the so-called "creepy wails" toward the end of "Gold Dust Woman" (Philly and NYC 1977, below) qualify as falsetto. They seem to be something of a different animal altogether (and regardless they are stunning performances well worth checking out).
What do you think?:
Philly:
https://www.youtube.com/watch?v=DZV9wSjOsD8
NYC:
https://www.youtube.com/watch?v=clDt4eTP3aU
Many thanks to all who have helped me with this endeavor. As TheWildHeart67 suggested, it is turning out to be something of a thesis but, as he also suggested, it is indeed floating my boat.
Thanks again.