prior incantantum... Mistake / Clue? I'm confused!

[bleckybecs]

No: HPFGUIDX 124214


I was just reading the thread about 'prior incantantum'.

The thing I'm confused about (now that I've just thought of it), is 
what happened to the AK that LV aimed at Harry? It was a spell cast 
by LV's wand, why is there no prior incantantum of any sort for this 
spell? Everything else appears to be accounted for (even if JKR got 
the order wrong in the original book), but this one should be in the 
middle of it all, shouldn't it?

I have no theories to offer, I'm just interested to hear what anyone 
else has to say, and apologies if I'm bringing up an old subject. If 
I am, can someone please direct me to the right place.

Thank you

Becky :)