The "As down the glen one Easter morn" version is certainly post-1916, because it has the lines "Or had he died by Pearse's side, or fighting with Cathal Brugha". The Pearse is Patrick Pearse, one of the 1916 leaders; Cathal Brugha was one of the 1916 officers, who later died when he came out from hiding with both guns blazing and was shot down; a little tiny man but a spark of bravery.