UseByDate Mth-yy + X mths, where Mth-yy is the creation date of the entry? Purpose is to give reviewers more information to determine whether a page should be touched/refactored, deleted or left alone. (e.g. pages on OO conferences of dates past)
The above thought came about when I encountered pages I am not sure whether the contents are still relevant. The syntax mentioned would provide a reference point relative to the creation date of the page.