group on person
insert a summary (sigma sign)
select the contactdate field
set it to a distinct count
set it at the person gfroup level
it will result something like
DistinctCount ({table.ContactDate}, {table.person})
create a running total
field to summarize= personid
type = distinctcount
evaluate = use a formula
DistinctCount ({table.ContactDate}, {table.person})>1
reset = never
place in report footer