2.1.837 Part 1 Section 18.14.13, sheetData (External Sheet Data Set)
a. The standard states that @sheetId index is an unsigned integer, with no additional restrictions on value, and that it is 1-based.
Office requires that @sheetId range from 0 through 65533 inclusive.
b. The standard does not define any order requirements for rows.
In Office, rows must appear in ascending order.