sgcBiometrics package adds a new feature for next 1.4.0 version, now you can Enumerate which Enrollments has sensor pool selected. This method works for System and Private sensor pools.

Before that, you didn't know if a biometric sample was already stored in your database except if you try to enroll fingerprint again. Now you can first enumerate which fingerprints have been stored in your database.

Enumerate Enrollments 

First call EnumEnrollments method and then handle OnEnumEnrollments event and here you will receive which Fingerprints are stored in your pool. Check aSubFactor parameter to know which fingerprint is (right thumb, right index...) and there are 2 parameters which show how many fingerprints are enrolled and the number of fingerprint passed to event.

Here a screenshot of demo application showing how Enumerate Enrollments works.