Lucky you!! But if you can test him fairly easily, might want to hold off on using the Libre's in case the rescue gets another sugarcat in who isn't quite so cooperative! Just a thought (I think they also have expiration dates but I'm not sure about that)
Carlton's looking pretty good! If you're going to use the Libre and/or can continue getting at least 4 tests a day in, you might want to consider switching to Tight Regulation. It's a more aggressive method but also means you can increase as often as every 3 days instead of waiting a full 7 days if he's not getting the numbers you want.
How's he doing otherwise? Our kitties are more than just their numbers!