Going back to when I worked for GM, there was a series of diodes in the alternator called a diode trio.
This was responsible for turning the battery light on. It was not all that uncommon for these diodes to fail.
In other words, the entire charging system was working properly, but the battery light would come on.
Not saying this is the case with yours or that it even applies to our vehicles. BTW, the diode trio was not