How to enable "All" option for selecting assignments at absence entry

According to the implementation guide, when "Allow assignment selection at absence entry" is enabled at the Absence Type level, there should be an "All" option to include all assignments (eligible) to apply the absence toward, but we do not see one. If the employee does not make a selection, it behaves as if they are selecting "All", but if they mistakenly make a selection first, they must highlight the field and delete it. It is not intuitive for an end user since there 1) is no "All" option as is stated and 2) even without the "All" option, they cannot