The Health Check pulse report derives data from the 'Daily' interval of the EC2 Instance Usage report (https://apps.cloudhealthtech.com/olap_reports/usage/instance).  The filter selection list in the Health Check report stems from the AWS Accounts that have Usage data present within this report. 

If an AWS Account does not have any Usage data present within this report, then the Account will not show as available on the filter selection list.