2.1.299 Part 1 Section 17.10.6, titlePg (Different First Page Headers and Footers)

a.   The standard says that if titlePg is not specified, the first page shall use the odd page header/footer.

If the evenAndOddHeaders element is true, Word uses the odd/even state of the start attribute on the pgNumType element to determine whether to use the even or odd header on the first page.

b.   The standard says that if this element is specified and no first page header is specified using headerReference, a blank first page header is used.

In Word, for all sections other than the first section in the document, if this element is specified and no first page header is specified, then the first page header of the previous section is used.