Inverter VTC , VOH and VOL definitions
It all depends on what definition of VOH is being used. Generally it is either the minimum voltage that is guaranteed to be a logic high, or the output voltage when the transistor is fully off (ie. Vdd or very close to it). Datasheets often specify a guaranteed minimum VOH. The actual VOH is expected to be higher, but is affected by supply voltage, input voltage, temperature etc. 

So before you try to use some value, make sure you understand how it is defined by the supplier of the information. If your textbook defines VOH as Vdd then that is what it is in that text.