Last January I blogged about a mathematical coincidence. For three Jewish kin, there are records claiming alternate birth dates approximately 20 days apart. Adjusting for the 12 days conversion between Julian and Gregorian calendars, this leaves approximately 8 days - which could be explained if one of the dates is actually the date of their Brit Milah. (Covenant of Circumcision).
I didn't mention it last week in the Amanuensis Monday notes, but Max Kruvand's Petition for Naturalization states he was born on August 22, 1897, and his record of birth in Lithuanian records states August 3. So it's now four kin. (Three from Lithuania, one from Poland.)
I am unaware of a religious tradition of observing the anniversary of a brit milah (Outside of Christian tradition - of course, the Feast of the Circumcision could have Jewish roots.) I know that celebrating birthdays was not considered appropriate in traditional European Jewish households. There was the superstition that it was tempting the 'evil eye'. Celebrating any anniversary connected to birth would likely be seen similarly. However, it is conceivable that the date of birth wasn't recorded in some family records, but the Brit Milah would have been, due to its religious significance.