2.1.374 Part 1 Section 17.14.25, odso (Office Data Source Object Settings)
a. The standard states that the maxOccurs value for the recipientData child element is unbounded.
Word limits the occurrences of this element to 1.
b. The standard says that the odso element provides information about mapping to MERGEFIELD fields.
In Word, the odso element provides information about mappings to built-in mail merge data fields, not MERGEFIELD fields.