For years I regularly saw "BPED: 14APR69" on important papers.
And not-so-important papers also, I suppose.
"Basic Pay Entry Date" was the Army term for what usually corresponded to your entry on active service, though for some folks who had certain types of deferred entry it differed.
I didn't particularly need to be reminded of the date.
For me, April 14, 1969 was the day I got out of bed in Edmonds, got dressed, and went to the Armed Forces Entrance & Examination Station ("AFEES") on 15th West in Seattle, where they examined me & entered me into the United States Army.
Forty years ago this morning.
They piled us on a bus, drove us to Fort Lewis, cut off our hair, gave us some unattractive ill-fitting clothes along with boxes to mail the clothes we had on back home, and things were under way.
Forty years ago today.