Undetermined...will have to dig more...

It is said that "The number printed on the back of the card is a "sequential control number." It is a number that was printed on your card and helps validate the card as a legitimate social security card. The codes are printed in red, black or blue ink. They are used by Bankruptcy Courts and the Social Security Administration, to prevent identity theft."
-Social Security Expert: Gerald, Esq

Source: https://www.justanswer.com/social-security/d9a20-asking-stamped-number-back.html

USA Today did a "fact check" and mentioned some scams to this regard...

https://www.usatoday.com/story/news/factcheck/2021/05/27/fact-check-social-security-numbers-not-linked-federal-bank-account/5219832001/