I used to work for a paint store that sold DuPont. We had their camera which they called "chromavision". Customers were told, like yourself, that it would match spot on. This simply isn't the case. We had several instances where customers did not want to hear that it would be close but for an exact match, they should leave a part for a day or two to get an exact match. Many colors also have various alternates, these will have the same paint code, but there might be four or five different variants of that color. I say all of that to say if you have a small spot you wish to blend in, take the smallest panel you can and leave it with them for a couple of days to get as close as possible. Even then it may not be so close that you could paint a fender off the car and install it and it match perfectly. Paints have changed a lot in the last ten to twenty years, let alone the last 40 plus and sometimes things get lost in translation. Hope this helps