no alert i know of grants prestige you might get items that give prestige when given to your league but thats around 3 not 300
I run a lot of toons through the seasonal alerts; and would get 300 Prestige for each daily. It is not happening this year for the Fall Seasonal. Duos 125, Alerts 300, Raids 400.
Originally all seasonal events did not give prestige. I know that last year a few did, but that can change with each seasonal return. Since they originally didn't give anything, you may need to get a reply from Mepps or a dev to know for sure if it is supposed to be there or not.
They "Fixed" it by granting 1 Prestige instead of 0. So you would have to run it 25,000 times to make 1 league proficiency that lasts 30 days.
Knew abut some getting only 1, was hoping that that was fixed as well, guess won't be smacking around any Emo Pilgrims this year