When you (Constant Contact) do one of your database updates, ALL my clients' campaigns suddenly show a new last_modified date. This makes the email campaigns query 'modified_since' parameter useless. The only way to find which campaigns were recently sent is to query each and every campaign to check the last_run_date.
This is not the first time you have messed things up with an update. This is forcing us to significantly increase the API queries we need in order to generate the reports we need.
Please add a new parameter to the email campaigns collection query for last_run_since or similar.
We did notice this change to the last modified_date on campaigns and we are looking at a way to make sure it does not happen again. I will be happy to forward this feedback to our engineers as a possible solution.