Hmm, I've seen a copy of an order which de Valera received from Professor Mac Néill - leader of the Irish Volunteers, and it clearly uses an Irish form of the name and not de Valera so the name was in use during de Valera's lifetime and was used by at least one person who wrote to him. I note also that the Irish version of Wikipedia uses de Bhailéara as an Irish form for de Valera. Also the Official record of the Dáil from 21 January 1919 uses the form Eamonn de Bhaléra - a slightly different version, but proof possitive (from an official source) that there was an Irish form of his name in use, in Ireland, during his own lifetime and by an institution of which he eventually became the leading voice see http://historical-debates.oireachtas.ie/D/DT/D.F.O.191901210004.html, another example "Gearóid Mac Phárthaláin: A Chinn Chomhairle, tá sé d'onóir agam an [19] Teachta Eamon ****de Bhaléra*** a mholadh mar Thaoiseach. Ní gá dhom cur síos go mion nó go sonrach ar a bhfuil déanta aige d'Éirinn, mar tá sé sin i mbéal na ndaoine." (18 February 1938, URL http://historical-debates.oireachtas.ie/D/0110/D.0110.194802180005.html)  As can be seen his name generally appears as 'de Bhaléara' in the Dáil records however there is at least one example of 'de Bhailéara' " Nach cuma le Teachta De Bhailéara ....."http://historical-debates.oireachtas.ie/D/0040/D.0040.193111180039.html" 18 November 1931. I am going to add the Irish version used by the Dáil to this article.