My understanding is that AKG did not factory match back then (although you can buy the new AKG mics in factory matched pairs, including the much inferior C451B). I heard that their reasoning was that their quality control was so good that they would all be close. That is second hand info, so I cannot confirm that.
Earlier in the year I bought a group of 10 C451EB's and tested each with white noise just to see how close they were. Same spot, same source. Not a perfect test, but worthwhile to help my curiosity. I tested each body using the same CK1, then tested them each with their own CK1. There were variances, but all were pretty close. I was actually pretty impressed since they were all around 40 years old.