It seems that the code for cats and dogs will sometimes change depending on the lot number. The manufacturer's website says simply to use the code printed on the vial of strips, but I've found online discussions of dog owners remarking on the code changes. The new vial of test strips I'm using are coded 11, and the last two were coded 4. There doesn't seem to be any wildly different readings with the new strips, so I think they are fine. I will double-check with the vet pharmacy to be sure.