- SSN from different ID space gets assigned to immigrants; when they become citizens they are assigned a new permanent SSN.
- SSN:s have a long and a short form; the short form which cuts off century information can be the same for someone who is 5 years old and someone who is 105 years old.
- When an unconscious patient comes in to the E.R. you don't know their SSN, so a temporary one is assigned for use in patient records. Such temporary SSN:s are not coordinated nation-wide so multiple patients may have the same SSN. In some hospitals they don't even have a local standard for ID:s. The staff just makes something up on the spot. It happens that the SSN they made up collides with a valid SSN for another person.
Danish SSNs doesn't have a long or short form, you used the seventh digit to do a table lookup to see if the person is born in 18XY, 19XY or 20XY. The date of birth is always ddmmyy, there is no long form. So if the seventh digit is 9, and the 5-6 digit is between 00 and 36, then you're born in between 2000 and 2036, if the 5-6 digits are 37 to 99, then your born in the 1900. But you need the published table to figure that out.
Last point, there is backup system for unconscious patients, but it should be the same across all medical records as these are somewhat standardized.
We don't do that. instead, we shove that extra bit of information into the digit following the last two digits through a table: https://da.wikipedia.org/wiki/CPR-nummer#Under_eller_over_10...
> SSN from different ID space gets assigned to immigrants; when they become citizens they are assigned a new permanent SSN
Having gone through that, my personummer didn’t change. Maybe that doesn’t happen anymore?
While this was abolished in the 90s, _some people still have these 'W' numbers_, ticking timebombs for anyone relying on them as a key.