I work with pivot tables all the time. But one thing that seems to be
inconsistent is the following:

When I select a field to be a pivot table's "page" (usually a column that
describes a year), it will sometimes allow me to check off multiple years I
want to look at, sometimes I can only view one at a time (one option of which
is "all").

How do I switch back and forth, particularly switch to the checkboxes so I
can view, for instance, 1999, 2000, 2001 and 2002, but not 1998 and 2003?

Thanks!