The list of PD Providers on the "PD Providers" page represents those that voluntarily signed up for an account, thus allowing them to promote their organizational profile. These PD Providers offer some form of professional development, but may or may not offer pre-scheduled trainings.
The list of Sponsoring Organizations located within the Filter represent any and all PD Providers who have offered pre-scheduled trainings (which have appeared on the Training Calendar). These Organizations may or may not have decided to sign up for an account in order to promote themselves on the PD Provider page.
For these reasons, the list of Sponsoring Organizations (under 'Search by Filter') may be much longer than the list of PD Providers on the "PD Providers" page.