Things are certainly looking up, Ellen. Congrats to you and Robbie! Usually we say that they need to have normal numbers( anywhere from 40 - 80 or so) for 2 weeks before they are officially OTJ. During this time, I would test during the day when possible - morning and evening and when you can during the day. It is fun to test before eating and then an hour or so after eating, as the food will be lowering their bg levels, indicating a pancreas that is functioning! Just get some tests and keep records. If he starts to climb above 100, you would be much more diligent.
I am sure you have heard from others that our kitties are always identified as diet controlled, not no longer diabetic. Many cats here will get higher numbers if they get into high carb food, even if they have been off insulin for a long time.