early army pension entitlement is a very complex subject and there are many lists and records at the PRO, (Kew). The rank, service and discharge of each individual meant that the pension could vary .. many were discharged to half pension initially especially if injured out. The following link gives you the background, remember that there are seperate records for commissioned and non commissioned ranks.
http://www.nationalarchives.gov.uk/catalogue/r dleaflet.asp?sLeafletURL=http%3A%2F%2Fwww%2Ena tionalarchives%2Egov%2Euk%2Fcatalogue%2Fleafle ts%2Fri2006%2Ehtm&lBack=-1
I am not sure what army would have been taking plunder after Waterloo but i guess it depends on what family stories you have. I think a non-commissioned rank would be shot for theft possibly