Slughorn's potions in first day of class

[Eddie]

No: HPFGUIDX 161118

Slughorn had several cauldrons of potions on the first day of class,
including Felix Felicis, which we learn later takes six months to
brew, and Polyjuice Potion, which we learned in CoS takes weeks to
brew (lacewing flies brewed 21 days & fluxweed picked at full moon).

So how did Slughorn acquire these potions with only 2 months notice?
(See LONG timeline at http://www.hp-lexicon.org/timelines/timeline.php )

Hardly important, but maybe it will be fun to speculate.

Eddie