As mentioned earlier in this thread your medal is not an official issue. Therefore, the question is was the medal made up to deceive collectors or was it Wall himself (or a relative) who obtained it and had it named up as you see it today. The chances are that we will never know for sure.
If the medal was meant to deceive it would have been safer (for the faker) to use the rank/name as it appeared on the medal roll. It is interesting to speculate whether Wall lost his original official issue medal and the one you now hold was an unofficial replacement obtained later on. Wall was still serving in the army till at least the early 1840s so he needed to have a Waterloo medal to wear with his uniform.
I have found the following reference to Wall's death which occurred on 12 May 1850 as reported in the Colburn's United Service Magazine for 1850:
"May 12, at Tralee Barracks, aged 58, Captain John Quin Wall, late 89th Regiment, and Barrack-Master at Tralee."
Paul