Since we should use the name that was known at the time the person was living ... should I change his LNAB to Guimare?
He took his mother's name as an identifier and Guimare anglicized is Wimarc/Wimarce/Wymarch. I also do not want to use ''fitz'' as a gender qualifier in the LNAB because he should be filio/filius/fillii Wymarcha (if I am recalling the "naming" translation for son of and daughter of in this geography & era correctly).
side note: which is why I really do not like using gender qualifiers in LNAB - to be correct one needs to know the geographic area AND the correct usage of the era.
edit:
First, the Last Name of the person as known during his/her lifetime should be determined. In this instance, I can find no sources (referencing legal and ecclesiastical documents reproduced in books— see links below) that this person used fitz during his lifetime. This was added to later literature and "fitz Wimarc" became accepted as a standard in the 1800's. In some sources found in the 1900's & later, "fitzWimarc" (as one word) is used, but is not common. (An internet search of "FitzWimarc" produces a handful of links. The only link dealing with Robert is a Wikipedia entry, which produces no source for the usage of "FitzWimarc" as a last name.)
To follow the Naming Style set forth by Wikitree - #6: the LNAB should be what was "known" at the time of birth or during the person's lifetime. Sources do show how this person was known during his lifetime.
Therefore, the addendums (#6.a.1-3) do not come into play. This is a case of "If not x, then go to y." Here, we know x, so y is not needed.
Addressing the particular addendum of #6.a.3 - regarding the usage of "fitz" falls under #7, the CLN, and should be the modern usage. In all but a few cases, the modern usage is "Fitz Wimarc" and "FitzWimarc" should be listed in "other"
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In A history of England under the Anglo-Saxon kings, Volume 2, By Johann Martin Lappenberg, Elise C. Otté, for a charter issued by Edward the Confessor — no gender qualifier is used.
here is a link to ''The English Language" that has his name in a legal document - no gender qualifier is used.
Which is one of the main reasons I am adverse to using gender qualifiers in the LNAB - to abide by Wikitree guidelines it must not be spaced, to use the naming as it was during the person's lifetime there must be a space.
Latin was used for legal documents at this time - to remain true to the name of the person at the time he lived, adding ''fitz'' to the LNAB is counter to using the name as he was known during his lifetime. A gender qualifier should be placed in CLN since that is how he is known in modern times, not during his lifetime.