Our SFDC has a custom object for License - it references a table for 10 professional licenses in 50 states that our clients could possibly have. I've synced the License object over, and I'm able to get some leads to populate my lists; but not as many as are appearing in SFDC. For instance, I get 2,000 "Nebraska Superheroes" from the smart list, but there are 7,000 SFDC records with that license. Some are duplicates, but they're showing up in both locations anyway.
New leads getting captured are going to new fields that specify license and profession. Marketo Support's solution is to map every existing client over to those new fields; which we are doing until we find a better solution. 1 person can have multiple licenses, which is why the custom object is important and can't be replaced easily with fields.
Thanks for your help,
Bryce