According to https://ro.wikipedia.org/wiki/Cod_numeric_personal Ilfov is 23

Please provide a source.

Check this CNP: 2691128470037

I mean provide a fairly credible source that lists counties and their codes. If that's a valid CNP, then maybe the whole algorithm is broken.

I see several online validators (validari.ro, wtools.ro, valideaza.ro, validare.ro) do indeed validate given CNP, but don't recognise the county. So my assumption is they don't check the county code range. When you generate a new one, however, for Ilfov, with the same sex and birthdate, you'll notice the county code is 23.

Ok, my mistake. I have an ID card for this person and it's born in Bucharest, district 2, and now living in Ilfov county (I missread). So I guess in 1969 they didn't respect the county code for Buc. sector 2.
So your algorithm is not fully correct. That's why I proposed the change.

So, do you have any suggestion for improvement? If you accept my change this CNP will validate but I don't know if this is the complete revision.