Admittedly I get a kick out of studying technical and/or arcane stuff. I recently came across a long paper published by the SSA under the title "The Story of the Social Security Number". At 20+ pages, more with reference notations, this was longer than I had expected, and it was much more detailed and interesting than I had expected as well. I finished it several weeks back so my memory of some details will fail me in my overview.
The article gives the very earliest history of how SS numbers were developed back in the 1930's (1937?), discussing the various plans and schemes proposed for the identification system...which is still in use today. There's discussion of how all this was done before digital electronic computers, only using mechanical tabulating machines and many clerical workers.
Strangely enough, they kept early records on...I kid you not...bamboo sticks with markings. Remember this was before the day of computer chips and memories; although there were certainly punch cards. The bamboo sticks were kept on big metal racks and contained each person's record of identification (but not their earnings record). They were kept in a sort of phonetic system and it was said that an expert clerk could find a particular person's record stick (out of millions of records, mind you) in less than a minute based the system. I find this amazing myself. This was called the "visible index", as distinct from other important database systems for personal records, the "numident" and the "alphident"
The background of why there are 9 digits in the SS number is given, and why there three groupings of digits and what they mean. But the article goes way beyond describing the numbering system and gets into many other interesting facets of how the SS system was developed. I really developed an admiration for the dedicated people who initially developed the SS system and created all the supporting roles in place. I can see that this early work remains in place even to this day.
I didn't know until reading this article the process involved in getting the SS cards created, printed, and distributed. In fact, there is now a limit on how many replacement cards someone may obtain. Since 2005 "individuals may only receive three Social Security cards per year and 10 in a lifetime". This is a change from the 1930's when workers mistakenly thought they needed a new SS number (and card) for each job they worked at! Talk about record keeping problems.
So where is this opus that I recommend? see https://www.ssa.gov/policy/docs/ssb/v69n2/v69n2p55.html
Interesting enough, I later came across a post at the Reddit forums about (technically-) permissible names for the SS systems; what special characters are permitted, name length, etc (I have read of a number of people having real problems with this sort of thing; not everyone is a "Smith" or a "Jones"). The relevant SSA rules for this are in the POMS ("Program Operations Manual System")...which many people might want to become familiar with. See https://secure.ssa.gov/apps10/poms.nsf/lnx/0110205125
If nothing else, two interesting articles for a rainy afternoon.