Vetsulin's typical action is a quick drop early in the cycle, then a rise at the end of the cycle and by shot time they are back to where they started. There usually isn't a big change in preshot numbers right away. Doing the vet test so soon after the shot really wasn't going to show much. There might have been some vet stress raising the number there and some variance between methods of testing.
Really, you pretty much got the same number, but don't know why unless you get some testing later in the cycle. Preferably by home testing, but when you take him to they vet get an appointment farther from the shot.
I highly recommend doing some home testing. My Cecil was almost killed on Vetsulin simply because of timing of the tests at the vet. The shelter would give his shot around 7 in the morning and take him to the vet once a week around 4:30 to be tested. The insulin never lasted that long so they only ever saw high numbers. He went up to 5U b.i.d. in about 2 months time. He got skinny, sick, wouldn't eat. They found him in the kennel pretty non-responsive one morning and took him to the vet 4hrs after shot, found him in the low 100s. After I started talking with the shelter manager we noticed the timing of the tests and are certain he was getting lower #s in the cycle where he should have been which in turn caused bounces to higher numbers that caused more increase in insulin and it just circled out of control. If the shelter had been testing him, or taking him to the vet earlier in the day, they would have caught the insulin's action better and not been increasing the dose like that. We did take him off of Vetsulin at that point and a month on Lantus (and into foster) he went off of insulin and remains OTJ almost 2 years later. He came down fast on the new insulin and if he hadn't been being tested, he could have been in trouble. I don't know if we slept during that first 3 weeks we had him.