This may help if I understand your question correctly.
Create a Formula field for the description.
In the formula editor, write something like this:
if {?Start Date} = '1' then "description of prompt 1"
else
if {?Start Date} = '2' then "description of prompt 2"
else
if {?Start Date} = '3' then "description of prompt 3"
else ""
Then insert the formula field into the report where you want the description to go.
Hope that helps.