Since you have sources and already are a member of our Project it's ok to add the profile Roelof. :)
The notification you see now, so the message that asks if you perhaps can contact a project working on these kind of Pre-1700 profiles before creating/adding new ones, is to try, and hopefully prevent, members are going to create duplicates with perhaps backwards projected or wrong last names based on just online genealogies or without any sources again, that all already are present and corrected here, we have/had a lot of Gedcom imported families with wrong or backwards projected last names that now are corrected and when someone tries to create these profiles with again the wrong last name the system doesn't recognize this profile as a duplicate...so for all Pre-1700 (and for Dutch the Pre-1811) it's best if you are not certain or can't find a family, to first contact a Project and ask if perhaps this family is already present at WikiTree..but you are already a Project member and know how it works, so in this case you can ignore the notification..
