Yeah, this way they can both be "right." 

Also, keep in mind that if a vampire were completely deprived of blood, with absolutely no way to get it, like if Erik were chained up without the potion, then they would actually die. I want the lack of blood to be ultimately fatal for them.

So between suicides and the fact that if not given the potion it would be fatal, I can see why Erik thinks the way he does.

A more accurate description would be that, "this procedure, if performed correctly, has never been fatal."

Sorry to split hairs about it, I just want to be sure we are on the same page.