This is a good and interesting exchange and I'm leaving the question open for a bit. And, adding my own comments to comments already made. I'm a professional librarian, not a professional genealogist but I've been researching ALL my families for about 50 years. One of my ONSs is because that family surname has, reportedly, 42 to 52 variants. I have no origins yet and within my own immediate family and a family cemetery there are 3 spellings; go figure. And, now I've adopted quite a few profiles....
I'm a rule follower, as much as possible, in all things, because rules simplify things, in most cases. What if there were no road rules? Chaos. While I don't subscribe to the notion that people are inherently evil, I do know that we're selfish and thoughtless; so rules are necessary. I like the LNAB rule, so birth or baptism surname; not always available. But that should be individual by individual so grandfather in Germany might have spelled it differently.
As far as contemporary surnames, don't bet on them not being changed either legally or not; a friend changed hers just because she wanted to.
As far as suggestions, I hadn't thought about the fact that they're called suggestions but I will in the future. I just "fixed" one where the marriage of the parents were in questions and still is but the son's marriage record shows the names of the parents so they're his parents. I doubt I'll figure out the multiple "marriages" of his mother.
"Official" documents, more preferred documents, are full of mistakes and, yes, whoever filled them out apparently never asked about spelling. I do collect signatures when I can find them and I do go by the sound of names rather than spelling.
Finally, I have built databases so I'm well aware of changing key data elements and we should not be casual or cavalier about doing it. It can have very bad consequences.
The person named in the question; her surname became Wormuth, with variants, one of my ONSs. Her maiden name, Fheling, also has variants, this spelling in question but that's her father's name in the record as well.
It's maddening sometimes.