Hi Netti
You are correct, Ancestry have indexed "Batt'n" as Bass. For anyone else looking for Edmund, he is recorded as "E" in 1861, and in 1871 as "Edmond".
I would be surprised if he was still serving in 1891 and 1901 because of his age. You do not mention 1881. If you have found him can you say how Ancestry have indexed him?
If he died in service his papers would have been destroyed 20 years later. But even so, as you know his battalion/regiment you should be able to follow his service using the Muster and Pay Lists -
http://www.nationalarchives.gov.uk/militaryhistory/army/step4.htm Starting in 1861 you could work back to find his enlistment. And working forward from 1871 you can find what happened to him. However, these are original documents and you or your researcher will have to visit Kew.
As Neil says he could have transferred to another battalion, or even to another regiment, and may have retired/died in either India or Ireland. What is the last definite sighting of him?
Ken