All men present at Waterloo were granted 2 years pensionable service, and that fact is shown on their papers. So if it's not mentioned then he wasn't there. And indeed he's not listed on the Waterloo medal roll, so we can be fairly sure he wasn't.
If he was in the 2/73rd all the time then he saw a lot of Empire service .......
Well the 2nd Btn was only raised in 1809 and disbanded in 1817 (when William was discharged) so before that he was presumably 1st Btn.
Their movements for you:-
1st Btn
1788-1806 India (including 4th Mysore War 1790-92, Anglo-French engagement at Pondicherry 1793, Ceylon Wars 1795-97, 5th Mysore War 1799, Polygar War 1801, 2nd Mahratta War 1803-05)
1806 England
1806-09 Scotland
1809-14 New South Wales
1814-17 Ceylon (Kandyan War)
2nd Btn
1809 raised in England
1809-13 England/Wales
1813 Sweden/Germany (Stralsund, Gohrde)
1814-15 Flanders (inc Waterloo)
1815 France (Army of Occupation)
1815-17 England till disbandment