In my experience with vegan meals on Intl C flights is mixed. I have always gotten the vegan meal requested if my upgrade cleared >24 hours. That said, I think the food is terrible. The salad is usuallyok, but the pile of barley/cous cous/oily veggies usually gives me an upset stomach. I ususally BYO and then pick at the food they bring.

As always YMMV