An interesting controversy: Sammons says she never published another song, although she says she wrote a few others.
It would seem she could offer proof she got the payment for the song's rights....maybe she has.
Even so, it's possible Parsons' version is a take-off of sorts, from what he remembers of her song; and may be within that gray area of being "inspired" by a previous work.
From what I've read of Buchanan's version, it's possible Parsons had his/Sammons' part of the song pretty much down, and Buchanan's contribution of a second verse was ex post facto, although he didn't realize it at the time. He thought, perhaps, Parsons was creating in the moment , as was he.... ;
   And, yes, good point+: even if they paid off Sammons, it doesn't seem right to hang your name on the song.
    I think it's easy to think the Stones stole stuff from Parsons during their sojourn in Texas; it's instructive that they let the Flying Burrito Brothers record "Wild Horses" before the Stones. Some say that was just a tribute to the country influence they got in Texas. But Jagger and Richards were/are notorious for lifting stuff from other people (ask Ry Cooder); so....
   If Sammons had a bunch of other good songs, I would tend to believe "Hickory Wind" was all hers. In the absence of more evidence, I tend toward the idea that Parsons took some stuff from her, the germ, the idea, of the song, ...not a complete plagiarization.
    It would be interesting to see some experts analyze if "Hickory Wind" is similiar in word choice, tune, key, whatever, to Parson's other work.... and obviously, he was a songsmith of the first degree (Hey, I claim that as a song title-don't rip me off.)
    and let's not forget to simply love the beeeeyOOOTiful song...