Did Slughorn's other N.E.W.T. students all get "Outstanding" O.W.L.s?

Question

In Harry Potter and the Half-Blood Prince, Harry and Ron initially believe they will be unable to advance to N.E.W.T. level in Potions, since Snape requires an "Outstanding" O.W.L. grade and they both receive "Exceeds Expectations." It turns out that Slughorn takes Snape's former position and will accept students with an "E" grade, so they are able to take Potions after all.

However, it seems that out of the 12 students taking Slughorn's class, all of them other than Harry and Ron have the required materials, suggesting that they knew over the summer they would be taking Potions:

"Now then, now then, now then," said Slughorn, whose massive outline was quivering through the many shimmering vapors. "Scales out, everyone, and potion kits, and don't forget your copies of Advanced Potion-Making...."

"Sir?" said Harry, raising his hand.

"Harry, m'boy?"

"I haven't got a book or scales or anything—nor's Ron—we didn't realize we'd be able to do the N.E.W.T., you see—"

"Ah, yes, Professor McGonagall did mention..."

So did all of the other N.E.W.T. students receive "Outstanding" O.W.L.s? Why aren't there any other students in Harry and Ron's position?

Answer 1

Probably

I see two possibilities here:

• Perhaps there really were no other “Exceeds Expectations.” Given the small class size, this doesn’t seem impossible. Don’t forget, most of the other students (eight of them) were either Ravenclaws (who might be expected to do quite well academically) or Slytherins (the perpetual targets of Snape’s favoritism, and who might even be receiving a bit of help from Snape on the side). It could also be that the distribution of grades isn’t necessarily normal, and that if you know what you’re doing, you’ll probably get an Outstanding, and if not Snape will make life hard enough for you that you will end up getting Acceptable or lower.
• It could also be that the other people who received Exceed Expectations were not interested in continuing, not having planned to take Potions, studied it over the summer, and so forth. People often don’t like to change their plans on short notice.

It might also seem that Harry and Ron might have missed out on some essential information, based on McGonagall’s surprise that Harry was not taking Potions:

“So, Potter, Potter . . .” said Professor McGonagall, consulting her notes as she turned to Harry. “Charms, Defense Against the Dark Arts, Herbology, Transfiguration . . . all fine. I must say, I was pleased with your Transfiguration mark, Potter, very pleased. Now, why haven’t you applied to continue with Potions? I thought it was your ambition to become an Auror?”

_{Harry Potter and the Half-Blood Prince}

However, I struggle to think of a mechanism by which the other EE students could have learned that Slughorn was teaching, and about his grade requirements, in time to get a textbook, while Harry and Ron were completely unaware.

Answer 2

I suspect that Slughorn made the decision to accept student with lower grades just to get Harry as his student. He probably made the decision just after he was hired, which I believe was close to the start of the semester.