HBP's potions discoveries - why keep them secret?

[potioncat]

No: HPFGUIDX 140723

Bibphile wrote: 
> It's not certain.  It's just that all ten other students already 
had 
> their books.  So either ther other Heads of House informed their 
> students earlier that Slughorn would be the new potions teacher and 
> would accept students with E's or they all had O's. 

Potioncat:
I thought the little surprise...Slughorn is Potions; Snape is 
DADA...was nicely set up. I suspected it while Harry and DD were 
talking to Slughorn. 

If JKR had been a little more realistic, she wouldn't have been able 
to pull it off. Think about it: before school starts the kids get 
their book lists. If they don't know what they're taking, how do they 
know what to buy? OK, so everyone gets the complete list and you buy 
according to what you plan to study. 

Does Minerva really not know until the first morning of school what 
the OWL results are? We're told she confirms the results that 
morning. That would mean the teachers for the upper classes have no 
idea how many kids are in their classes...which at least for Hagrid 
seems to be true.

We took Snape's first class speech in OoP very seriously. He claimed 
to have a high pass rate and gave a look to Neville and Harry. So 
nitpickers that we are, we came up with percentages and numbers; we 
decided or at least discussed "high pass rate compared to what?" We 
were ready to have our calculations confirmed.....but we didn't get 
it.

We've no idea how what the results were for any class in Harry's 
year. Out of the 40 named students, 12 are taking Potions, but that 
doesn't tell us much. We don't know if Neville passed Potions (Do 
we?) We don't know if Snape looked at the numbers and visited his 
wrath upon any who failed.

We do know that Snape wrote the potions instructions on the board. I 
don't recall if we ever see the students using books in class. He 
does give a fair amount of research type homework. It's possible the 
potions texts (I think Snape assigned two) are not for specific 
potions but rather for properties of ingredients or potions in 
general. We know that Hermione did much better at potion making when 
she followed the instructions on the board than she did following the 
instructions from the book. So I would think he was teaching his 
improved version of potions.

Maybe, if Snape lives, he'll publish that Potions book. He'll have 
lots of time in Azkaban.