We all do at first. I remember being pretty pleased when I felt confident that I had worked out the difference between Charles Stewart (Castlereagh's half-brother, under-secretary for war, commanded a cavalry brigade under Moore and was Wellington's Adjutant General until he went home in 1812 and was then appointed ambassador to Prussia - how's that for a cv); Charles Stuart (diplomat, minister to Lisbon and worked closely with Wellington; later ambassador to France); and John Stuart (who won the battle of Maida in 1806). Also between John Murray (who commanded a brigade in the Oporto campaign and the inglorious expedition to Tarragona in 1813) and George Murray (Wellington's QMG throughout the war except 1812). And please don't mistake Alexander Gordon (Wellington's ADC, whose letters I edited) with Col James Willoughby Gordon (who was an influential figure at the Horse Guards and came out in 1812 full of plans to set the army's staff to rights, but made a sad hash of it and soon went home).

You might find Wellington's Brigade Commanders. Peninsula and Waterloo by Ron McGuigan and Robert Burnham helpful for untangling the complexities - it gives really good short biographies of the soldiers who constantly appear in accounts but have seldom had biographies of the own. Also S. G. P. Ward's Wellington's Headquarters has invaluable appendices giving summaries of the careers of all the officers who served on the staff.