Snape and Lily - school connections?

[Judy]

Snow proposed that perhaps Snape had trouble in Potions until Lily 
helped him.

I said: 
>> don't think I can handle the idea that Snape needed help
>> just to pass potions! I think canon is pretty clear that Snape --
>> whatever else he may be -- is excellent at potions.  He made the
>> Wolfbane potion, which Lupin says few wizards can do....

And Snow replied:
> Very good point about the Wolfsbane buttttttt
what if Lily were
> already working on that particular potion before her demise? 

My internet connection was down last night, so I was working on a 
post about this while offline.  Now I see that many of the points I 
planned to make have been made for me!

Eloise pointed out that we now know that neither Snape nor Lily 
invented this potion; it was Marcus Belby's Uncle Damocles.  I must 
confess I was disappointed to learn that Snape hadn't invented the 
potion -- but as not as disappointed as I bet Snape would have been, 
if he were a real person and someone else came up with Wolfbane 
Potion.

Pippin brought up that Snape had been writing potions recipes in his 
Advanced Potions book since at least 5th year, before he would have 
been assigned that book as a text.  This also suggests that he was 
quite good with potions  - why would he be using a textbook from a 
more advanced school year, if he were bad at the subject?

Also, in CoS Snape says he will make the potion to cure 
Petrification, using the school's precious supply of mandrakes that 
Professor Sprout has been growing for months.  I don't think 
Dumbledore would want Snape to use the mandrakes unless Snape was 
very good at potions.  (We don't actually know whether the Mandrake 
Restorative Draught is hard to make, although given that Lockhart 
brags about being supposedly able to make it, it probably is.)    

I also think that, to be good at teaching potions, Snape would have 
to be very skilled with them.  Copying from a friend back in one's 
teens just isn't going to give the type of knowledge Snape would need 
to be a successful potions professor. Now, we do know that Dumbledore 
sometimes hires incompetent teachers -- Lockhart, for example.  But, 
everything indicates that Snape is not in this category.  Even 
Umbridge can finding nothing to condemn in Snape's teaching -- other 
than that she feels the potions he is teaching students are too 
powerful and advanced. 

In regards to my general claim that canon states Snape is good at 
Potions, Snow said:
> Canon, did you say Canon? You wouldn't be referring to the fact that
> Tom Riddle's Mother had a brother that was imprisoned for murders he
> didn't commit? Canon can only take us so far with this Wondrous
> Woman, and then you're on your own. >bg<

But Morfin as the murderer of the Riddles was never part of canon.  
The *reader* is never led to believe that Morfin killed the Riddles; 
it is just the incompetent fools at the Ministry of Magic that ever 
believed this. Yes, JKR likes red herrings and misleading 
clues, but IMO, it's not her style to have Snape look brilliant at 
potions for 6 books and then in the last book suddenly spring on us 
that he isn't.  She usually drops hints much sooner than that, and 
typically resolves those sorts of minor mysteries within one book. 

-- Judy, seemingly under an Imperatus Curse that forces her to defend 
Snape