The name fields in Wikitree don't work well for European Aristocrat profiles, and one specific problem I noticed is the derived fields apparently stored/available, and last name fields should have a display flag like no middle name which also suppresses them from the derived names.
From the api for King Charles I:
"ShortName": "Charles I Stuart"
"BirthNamePrivate": "Charles I Stuart"
"LongNamePrivate": "Charles I Stuart"
"LongName": "Charles Stuart"
"BirthName": "Charles Stuart"
In this case he should be something like:
Short name: "Charles I"
Long name: "Charles I of England"
Basically PN or PN + CLN.
The main thing I think that will help is a flag to suppress LNAB Display and suppress OLN display - kind of like the "no middle name" button. For another example, if you look at his wife Henriette-Marie (why does she have a dash in her PN?) she should not have "(Bourbon)" in her derived names and she was never "formerly Bourbon" nor "aka of England, Scotland and Ireland". She is known as Henriette Marie de France or Henrietta Maria of France, with a preferred short name: Henrietta Marie. (NB: she had other "short" names such as Maria, Queen Mary...)
This would allow a more accurate display of people who do not have surnames (e.g. Henrietta Maria), or did not use their surnames (Charles I) and seems relatively easier to accomplish.
In addition, a "European Aristocrat" flag might be useful too. If we go back to Henriette Marie she might have tool tip that explains why there's no surname displayed. It might also take the place of the surname flags or simply do the same thing but indicate the reason. There are other well documented name problems with Suffix, Prefix and Nickname, which might be fixed with either access to the derived names, new derived names, or new fields activated with the flag. Thanks!