In business practice, this comes up a lot.
For example, in credit scoring say you included a set of marketing sources as a variable, odds are new partners are going come into the pipeline after you created the score.
In general, with infrequent categorical levels, say those with under $n$ examples, we recode them as "Else" and make that the reference category in the logistic regression
Pragmatically speaking the real question is how frequently do new categoricals appear and what proportion of the population are they.
If they are infrequent you can code them as "Else". This is not mathematically optimal but from a rubber hits the road standpoint it functions as a workaround.
If they are high volume however, you should need to create a new score to include them.