How recently did SS write in Potions book?

[potioncat]

No: HPFGUIDX 141726

 
> CV: Apparently not. Teen!Snape used sectupsempra on James.
> 
> Snape's Worst Memory (p 647, US ed.)
> 
> "Bad luck, Prongs," said Sirius briskly, turning back to 
Snape. "OY!"
> 
> But too late; Snape had directed his wand straight at James; there 
was 
> a flash of light and a gash appeared on the side of James's face, 
> splattering his robes with blood.
> 
Potioncat:
I thought I was the only one who thought it was the same spell! Canon 
doesn't say. I assume that Harry's spell did more damage because of 
the emotion behind it.

I know in posts downthread the question comes up: how did Snape 
practice these spells? Now, there's something I don't want to think 
about! But he also had to come up with a "cure" and he seems to have 
done that pretty well.