Interestingly he was logged in the Cemetery Book (on display at Carnton and composed by George Cuppett at the time of the re-burials) as N. H. Bishop, so even though the first initial was incorrect there is little or no doubt it was/is Col. Bishop. Consider that when Cuppett was digging up the dead 18 months had passed since the battle and many markers were rotting, defaced, or in otherwise bad condition. I can see how if Bishop's original wooden marker was deteriorating he (Cuppett) could have written down the wrong first initial. Then again, it could also have been a simple transcription error. The sad condition of the original markers is why some 550 soldiers buried at Carnton are logged as Unknown.
Eric