I've no book handy to check, but I believe that the rules don't preclude using the bonus to learn a spell that you could not otherwise learn (alhough I feel that they should).
I'll look it up for you tomorrow morning if no one gets to it before then.
According to the rules the lab bonuses can be used to create something that you can't otherwise create.
The reason that I dislike this is that is says that are certain things that a character can accomplish in one season when he's sleep deprived and befuddled that he can not accomplish in two seasons of being clear headed.
Among these things are: reinvent a spell that's slightly higher than your normal lab total from someone else's lab notes and create a charged magical device of extraordinary power.
On the other hand I do appreciate the simplicity of the rules that's gained by this.
You could always require the magus to translate the lab text he produces from such a season as if they'd been written by someone else: "What was I smoking when I wrote that?"