My ancestor has 2 birthdates, which one do I use? ?

His headstone reads 1891-1956. His death certificate says he was born 25 June 1891. However, I have found a WWI Draft card that William filled out in 1917 and he reported his birthdate as 23 June 1892. The 1900 census also reports "June 1892". Which date do I use in my records??? I'm inclined to use the earliest records and make a notation in my records about the other date. That would be most professional or official, right? Need some feedback.... please.