CD4 Color Film Developer

It's very unsicentific of me but I have had excellent results mixing ECN-2 chemisty (uses CD-3) from mostly dry bulk chemicals simply using Kodaks published formula. I then tried just substituting CD-4 in the ECN formula to process some C41, because I found some 800 speed 5 year old rolls while cleaning. (shame on me) The color was correct! looked about as good as I would expect if I sent it out to a consumer lab and it wasn't 5 years old. I'm about to test this on a fresh roll.

From what I hear there is a difference between CD-3 and CD-4 both in molar weight and in activity. Your colors may have looked great because they have to dialed in after a scan, but what do the shadows look like?