How does Snape know?

[potioncat]

No: HPFGUIDX 113529

I'm reading back and forth between GoF and OoP and something jumped 
out at me.  In GoF Crouch!Moody performs the Forbidden Curses in 
class.  Harry proves adept at resisting the Imperius Curse.  A long 
time ago, our group discussed whether DD knew about this.  We ended 
up with two disagreeing camps as I recall.

In GoF in the graveyard, LV performs the Imperius and again Harry is 
able to resist.

In OoP Snape is starting Occlumency classes and comments that Harry 
has some skill in resisting the Imperius Curse, comparing it to 
resisting Legilimency.

How did Snape know Harry could resist Imperius?  If C!M was working 
as Moody under DD's instructions, he could have reported it DD.  But 
why would C!M tell DD?  And why didn't LV know that Harry could 
resist it? Do you think Crouch!Moody forgot to tell him?  

So, do you think DD told Snape?  I wouldn't think C!M did.  They 
didn't seem the type to sit around and discuss students with each 
other. Do you think Snape learned about it from a DE contact who 
told  him about the graveyard events? Or, was Snape there afterall?

Potioncat: once again full of questions and no answers!