In the United States, every citizen has a social security number for income purposes. It's a 9-digit number. This began in 1935, though I was surprised to learn from wikipedia that until 1986, most people only got their number around the age of 14. Today, everyone gets it at birth.
Did the Soviets also give everyone a ID number? Was it a 9-digit number? 10-digit? A 7-character alphanumeric sequence?
I searched for this on wikipedia's Passport System in the Soviet Union, because I know they used internal passports. I looked at both the English and Russian versions of the article, but could not find examples of ID numbers.
I did of course also google images and found this:
The first entry appears to be a birth date because I see the number "1946". There is a printed number, "I-T3 No. 681711". However, a 6-digit number can have at most 10^6 = 1 million unique entries. The USSR around the time of the war had 170 million people, and around 1990, around 290 million people. So a 6-digit number is nowhere near enough to hold that many unique ID numbers. You would need a minimum of a 9-digit number.
This makes me think the internal passports were not issued to everyone, only certain people of whom there could only be a million or less. But then, the "I-T3" could be part of it?
(Edit: It's actually I-TЭ, where Э is the 30th letter in the Russian Alphabet. TЭ is a district code. The I is a roman numeral but as of yet I don't know what it really means.)
Is there some ID document given to everyone, that gives you a unique ID number? I looked at birth certificates too but came up emtpy.