Zip up ceiling
I did some touch-up painting on our house where we've lived for 3 years. The last owner left cans of the paint that was used as well as the "formula" used to mix them. I've done a couple touch-ups before and found that some of the paint had changed a little. One kind looked less glossy and didn't match 100%. But it wasn't too noticeable. (I'm guessing the old paint is at least 4+ years old)
I just did some touch-up in the bathroom and it DEFINITELY doesn't match well. Not that the color is wrong, but the existing painting has faded quite a bit so the old paint is much darker. Now I'm in trouble with my SO. This room is very complicated; there is trim and chair railing (I think it's called) so there are 3
colors in there.
Some paint stores that cater to the commercial trade have good color scanners that can match the color of faded paint. Those stores will also give good advice on how to match the gloss as well.
You'll have to do more painting over the spots you did, but if you can take a chip of the original paint in, those scanners are often calibrated to match the lines of paint a store carries, and you should be able to refresh an old paint job without having to do it all over.
If the store recommends one brand of paint for the purpose, heed their recommendation. All brands change their formulas from time to time, and the original paint may now be different that the stuff on your wall.