Signal Conversion 36V to Logic Level with Zener Diode
Zeners, particularly low voltage ones, leak far more than the CMOS input (1uA is a very loose specification at high temperature). For example, 100uA at 1V for a 2.2V zener. 

So I suggest you lose the Zeners and use a different kind of clamp. For example, a diode clamp to a 2.5V shunt reference for each input. You only need one 2.5V shunt reference, but each input needs the series resistor and diode. 

The other problem is that if the input is left open (not grounded), there is no reason for it to go to logic low, so you really need a resistor to ground on each input. You could use 470K resistors to ground and varying values for different series resistors, but the first one would call for a relatively low value of resistance, perhaps 100K. 

Edit: 

Clamping scheme: 







simulate this circuit &ndash; Schematic created using CircuitLab

(not shown the Vref to cathode connection on the TL431 to set the voltage to 2.495V nominal). 

The TL431 can clamp significant current (up to 100mA total). Input voltage will
be one diode drop plus 2.5V. 

Using the supply voltage runs the risk of causing it to rise out of regulation as most regulators cannot sink current and also you would have to use Schottky diodes, which are relatively leaky compared to signal diodes such as the 1N4148/LL4148.