Someone whose "dies natalis" is NOT in January is the
Doctor of the Church,
Saint Thomas Aquinas.

He was born to eternal life during Lent.
But the Church of Rome
decided that so essential a Christian thinker
ought to have a solemnity/feast-day
that was NOT during Lent,
the better to be celebrated with due pomp and circumstance.
That's bureaucracy for you ...
so his feastday is in January.