If the book formula isn't working, maybe the color of the card will be enough.

If the spray out card is as good of condition as it appears, and as accurate as it seems on the computer screen
(I own a QQ1 '68 charger that the exterior was repainted long ago.....your spray out card looks identical to the inside
of my trunk lid)......Just an idea but it might be good to check with local
suppliers to see if they have whatever the latest camera/spectrometer system is, and give that a
try with a pint or so to see if you like it.

I had good results with the PPG prophet system several years back/aroudn '06... which looks to have been replaced with RapidMatch.

https://www.paintmanagerxi.com/XI/rapidmatch