Va seems to have been well-defined on this thread. Theoretically, one can apply full control deflections and not break anything. There are some exceptions, well-noted previously.
Vb would be a max speed / mach where you can encounter a max gust (defined by FAR 25 - I don't recall the figure, maybe 50 fps) and not have any structural damage - theoretically. This doesn't necessarily relate to full control deflection, as as such is not directly related to Va. The speed is usually quite a bit higher. Indeed, I don't recall flying an airplane on which both were defined. I suspect that's due to different certification rules. I ain't no expert, but I think I got this right.
And note the liberal use of the word "theoretically". Y'all be careful out there ...
