I think you can only use sourcing & filtering based on fields on the list/record type on the field your trying to filter. So in your example I’d trying to filter down the vendors list/record you would need to use a field on the vendor record that is comparable to a field on your subscriber record Right now it does not look like you have a field in common between the 2 But, Can you use a script or workflow to source the subscriber class onto the vendor record. Then filter by subscriber class?