I'm not familiar with 9500 but Pro-10 printer driver has adjustments that might, with passage of time or electrical events (unreliable source, lightning etc) might abandon "zero" settings.
Very closely studied visual comparison of Pro-1 Vs Pro-100 prints: Pro-100 rarely comes close to neutral B&W with Canon OEM ink and they shift significantly depending on light source: Pro-10 PIGMENT and presumably Pro-1 pigment shift no more than a silver print would under all sorts of light...