You can probably do this with a SUMPRODUCT() function that includes
double unary operators, but that assumes your data is laid out in rows
with some kind of indicator of a recertification. Can you post a
sample of your data? Also, when you say "within 60 days" do you mean
before *and* after 1/6/06? And is 1/6/06 going to be a dynamic date
that changes every day, or every spreadsheet?