Please correct me if i am wrong (I am sure someone will!): Once you are a registered sUAS pilot under 107, i believe you are always one. However, if you are out of date (out of currency), you no rights under 107 until you pass the re-cert test. it doesn't matter how long you are out, once you pass the recert test you can fly commercially again. Finally, and this is IMPORTANT, your 24 month period starts from WHEN YOU TOOK THE TEST, not the date of issuance of the cert. At least this is what i learned from the 107 course I am taking now.