Early 2014 we stopped producing new weekly sets. After completing the currently displayed set you will be offered any previously uncompleted sets in reverse chronological order all the way back to the first set, Hypnofrogs. There are 168 in total.
Starting in version 3.0+ you can now skip sets by tapping the Get New Set button. The app will offer any uncompleted sets in reverse chronological order.
Also in version 3.0+ all completed sets were lost and will need to be re-completed. The rewards for the sets can be earned again when re-completing sets.