Yep, the bluish face it the top. But it does not mean the sides get oriented in a way that makes the sense in THIS particular rotation.
Check it yourself — choose Isometric Right (or the default Off-axis Front) and see how the C and other sided get oriented 'correctly'.
So what’s correct for one position in 3D, can be off for other angles. And the solution is to either rotate the shape how it makes sense for your current purpose, of rotate the symbols...
Classic 3D doesn’t offer rotation of the 3D pivot and probably never will... after all, Ai is not a a 3D editor.

I assumed that in the rotation preview cube, the bluish face was the top
If the dark grey face is actually the upper one, it behaves correctly
but
in the position presets, "Isometric Top" depicts the blue face up while "Off-Axis Top" shows the dark gray one up
that's a little confusing

Ah, I see. Bevel has nothing to do with it, you just flipped it over on its head.

The object you are having has an ambiguous shape. Illustrator has to assume the start of coordinates, and it does not match the one you assumed.
Take a look at the image attached: I made a copy of your object and just rotated it. The original shape is now facing down, and the extrusion goes up. This makes the positioning of the pages correct, and the only thing you have to do is to change the order of mapped surfaces.

I think that the problem described is this one with the file I attach
Graphics inside symbols are placed correctly, but when applied to the extruded path, they appear rotated 180°
The face to which it is applied is the front one and not the rear one

Please provide a test file.
I can see the image you posted at forums, but the whole conversation is does not provide much details on what is happening and what is wrong.
I guess you and Monika were talking about different means. Bevel has nothing to do with orientation of the mapped symbols.
Again — please start with showing the file. It can be a simpler file, with only this object within.