"Thenadays" was 1969, a few years after K Frame's DOB in 1965. I reckon that birth-issuance came some time between those years and may be dependent on locale.
Also, if you were born before the birth-issued starting time (whenever that actually was) you may not have needed one until you started work... which was the case with me... or some other circumstance generated the need. I seem to recall when I got mine there was mention of it being "for retirement." I dunno, but it seems to me that a lot of ladies who never worked may have had to apply for one later in life. I guess.
The ten-digit numbering system ( 1234-56-789[10] ) without replacement allows for 9,999,999,999 individuals to be "numbered," and the U.S. population is only 341,936,399 at the moment I looked, so there's plenty of room for more.
Terry, 230RN