And that's why the thief debate happens.That be because D&D is a choose your own adventure system and doesn't have a singularly solid source reference. Its a stew of many source references. So, there is not A,B,C choice, but a whole alphabet of them.
Because D&D pulls from sources where the thief is much better at thievery than the fighter, sources with the thief is just as good at thievery as the fighter, and sources that the thief is wildly better than the fighter and is obviously supernatural and ability.
The thief is added but never answered "which thief".
Well it did.
Just that few knew the references to agree which what was added.