Colorimetry problem after printhead replaced. HELP!

Hi, I appreciate some help. The situation is: An HP Latex 570 printer, color calibration satus ok, non expired Magenta / Yellow printheads with 6 liters ink used, same vinyl, same profile and pass mode, same print job and then we achive a color (oranje color). Then, after 3 weeks, we replaced the two magenta / Yellow printheads at same time and then after color calibration, we aren´t able to achive the same oranje color, no matter what we do! The job file was riped with the same icc profile. I've done some test to simulate this situation, and I understood that the old printheads aren't able to fire the same amount of magenta ink, so we are not able to achive the same color. My doubt/question is: Is there any ink usage limit of printheads before we start to loose the color reliability even with the colors calibrations available? Can it be some kind of issue at my espectrophotometer? Does the firmware, after color calibration, shouldn't be able to force the old printheads firing the same amount of ink, or simply reject the printheads when they aren't able to do it? I will post some pictures asap. Bruno Carvalho