This is inspired by the result of an error report run on King Charles VIII of France (Valois-273)
Many pre-1600 profiles with a Wikidata counterpart trigger errors 555 and/or 558, obviously because one profile uses the Gregorian calendar and the other uses the Julian one, resulting in a (roughly) 10 days difference between the dates.
I understand Wikitree policy is to use Gregorian dates whenever possible. I don't know about Wikidata. Some dates entered into Wikitree may be Julian where they should be Gregorian, but I'm not sure. Right now I tend to tag those errors False when they concern a profile before 1600 (roughly) and the difference is about 10 days, with a comment like "Julian/Gregorian calendar ambiguity".
Could the error report be adapted to avoid raising false errors, or a more comprehensive explanation added to the help page for these two errors? I'm not sure what the appropriate solution is and of course the issue is complex since countries switched to Gregorian at different periods (beware of Wikidata dates imported from Russian Wikipedia !). Here is a list: https://en.wikipedia.org/wiki/List_of_adoption_dates_of_the_Gregorian_calendar_per_country
(Adding euroaristo and notables tags because of the Wikidata issue).