Board Thread:Theories and Speculation/@comment-28550406-20160601140633/@comment-734582-20160602065840

Lulcielid wrote: Except that Do we really need to know that? Is there a meaningful reason to know that (Tsunade´s surname in this case) outside of wiki archiving sake? What would change knowing that? Absolutely nothing.

Considering none of the Sannin have surnames, it's likely that Kishimoto wanted to show them as truly ninja beyond clan and village.