Todays paint mixes will not match perfectly. It's takes a good paint mixer to get it right. The paint stores have spectrometer cameras
that can in your case take a pic of areas on your car that still have the original paint and come up with a mixing formula. The camera only needs at least the size of the coin of a quarter to take a pic.
Also, request the mixer do a "spray out" on some cards to see how it compares to the original paint spot. You may need to pay a little extra for this but it's well worth it.
Also, what plays into the game here is adjusting the spray gun that will be used to spray the car. Adjusting fan width, air pressures, distances of gun to paint surface, speed of gun movement. All the above will affect
how dark or light the paint will come out.
I just had this issue recently when I had to match an imron paint color
because no one sells imron anymore. I did a very good match with an Omni single stage. I tuned my Binks spray gun to those adjustments stated above. About 30 to 45 minutes of trial and error I got the paint looking like the imron color.