2.1.1441 Part 1 Section 18.104.22.168, dLbls (Data Labels)
a. The standard does not place any restrictions on when the child elements of the dLbls element can be specified.
Office does not allow delete, dLbl, leaderLines, numFmt, showLeaderLines, spPr or txPr child elements when the parent is not ser.
b. The standard does not specify an override behavior for data labels.
Office interprets data labels to have a hierarchical order of overrides. A dLbls child element of a series overrides the dLbls element of the ancestor chart group. A dLbl element overrides the dLbls element of the ancestor series or chart group.