I know it may look simple or ridiculous but I'm really not sure.
Not at all - the only silly questions are those we don't ask when we don't know the answer ...
Consider an aerobatic aircraft flying upside down in level flight - the wing sees a "negative" angle of attack. The forces are similar for both cases (positive and negative AoA) albeit that the fuselage attitude will differ, depending on the wing rigging incidence.
Often, the text books tend to show only the positive CL curves but you can find graphics for a wider AoA range. For instance,
https://www.sciencedirect.com/topics...ft-coefficient
(you need to scroll down a bit and there is a useful graphic on the RHS of the page).