I've been upgraded on gifted EVIP for tickets purchased long before the EVIP is applied.
I have no idea about success rate. I assumed like some other programs if all 4 are on the same PNR there must be 4 upgrades available at the same time. So if they only release 1 or 2 at a time the entire group will get skipped over.
Since this is AA specific question, I alerted the mods to move to the AA forum for you for more exposure to those with AA experience