Marlin mentioned useing a prophet, ie: a scanner to read a small chip of your paint. That may be a good option as many times paint jobbers will cross reference the old codes to new ones as some of the old mixing codes being laquer, don't have a BC/CC mixing code. Those newer mixes while close are not the same. Also BC/CC is going to be brighter, and have more color depth due to the clear coat. That alone will make it look like a different shade.
www.autocolorlibrary.com has chips, although they are hard to see.
I'd get a scan, and talk with a jobber who has experience in mixing older shades. Most places do'nt. Schonye