So true. One question on my real deal I literally only ever saw in my anatomy textbook (not even class slides or test). This happened with several NBMEs/UWorld Q's too, where I hadn't seen the info anywhere else except class-studying resources. Anatomy really is something you just don't really study for that much for Step 1.
OP, FA is the gold-standard resource. If it's not complete, that's because the material not included isn't high-yield enough. If you memorize every single word of FA, only then should you move on to a more detailed resource.