Not so easy. 4, 7, 9, 11+ are hard finds (except maybe 12). Congratulations on the ones you have acquired.
In my opinion, no matter what series you choose, there is always one or more that are hard. For instance, Griswold small logo would ideally include the 10 grooved handle. I think there is 1 known.
Enjoy the hunt, enjoy the cooking, and just keep at it. The feeling of success to find a rare piece is much greater if it is long-sought vs stumbled on it without ever recognizing it. Of course, the deferred day of recognition does deserve mention but it's not the same.