Pivot Chart - pages
 

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

When I select a field to be a pivot chart'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?

Thanks!