3rd paragraph of office:value-type reads:

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The value type of each of these elements shall be specified. If the value type is not string or if the <table:table-cell> element content differs from the value of the element, the corresponding Value Attribute(s) (Table 14 - Value attributes) shall contain the value(s) of the element.

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First, the mandatory appearance of type should be specified at each element and not here. So lose the first sentence.

Second, I don't know what the second element in "if the <table:table-cell> element content differs from the value of the element" is making reference to? How can cell content differ from "the value of the element?"