Thank you. As I said, it's just a tiny mistake, not a significant one. But it can lead to annoying inconsistencies in the storytelling.
However, it could also be that this isn't a mistake:
1. In Medieval Timess, there were certainly cases where noblemen had their children raised by someone else. One case is even legendary: the famous "King Arthur", if he ever existed, is raised in all legends not by his father Uther, but by his loyal knight Hector/Ectorius.
2. On the other hand, likewise, noblemen and other powerful people didn't always take fidelity so seriously and slept in the beds of the bourgeoisie. So it could be that Lucrecia cheated on her husband, meaning Ophilia isn't by Pietrov, but by Zachary, and Ophilia doesn't even know that.
Both ways would then raise the question of how Thomas knows about it.