When an artist changes their name (as opposed to starting a new project), the existing MB Artist with the old name is supposed to be renamed to the new name.

For artist credits, the edit system facilitates (not) changing the old names to the new name:

Please select the artist credits that you want to rename to follow the new artist name.

This will enter additional edits to change each specific credit to use the new name. Only use this if you are sure the existing credits are incorrect (such as for typos).

Keep in mind artist credits should generally follow what is printed on releases. If an artist has changed their name, but old releases were credited to the existing name, do not change the artist credit.

For relationship credits, there is no such facilitation.  Any relationships that do not have credited text will automatically use the new name, which is almost always not intended.  The edit system needs to have the ability/option to fill in all blank relationship credited-as text values with the old name when renaming the MB Artist to the new name.