"And it takes six months . . . You've got to let it stew . . . ."

"Typical," said Ron.

They're referring, of course, to Felix Felicis, concluding it would be too much of a bother to try and make more of it for themselves because it's complicated to make and also not meant for those who are impatient or poor at planning ahead.

We also know that Polyjuice Potion takes over a month to make, and so does Veritaserum.

Weren't all three of these potions on display in the very first Newt Potion class in HBP? And hadn't Slughorn just arrived at Hogwarts much more recently than even one month?

So, did Slughorn make these ahead and store them somehow? Did Snape make them and Slughorn just use them? How would that work? "Professor Slughorn, I've prepared these potions for my NEWT level class but now that you'll be teaching it, why don't you use them?" From observing them, I'd say the two professors have different enough teaching styles that Slughorn wouldn't use Snape's lesson plans but would teach the class his own way.

Harry is convinced that Malfoy stole the Polyjuice potion for use in having some ready-made but inobtrusive guards for his secret activities. How much potion would that require? Surely more than could be stolen in one shot in a classroom filled with students.

So did Slughorn make the potions ahead of time and pack them away in his suitcase to bring to Hogwarts? Or is this just a case of Jo's maths weakness striking again? And did Draco steal the Polyjuice potion? Did he steal any of the others as well? We see no evidence that he used Felix.

Hmm . . .