I don't think it's possible to come to a consensus unless riot themselves come out and clarify it.
Bcoz every Fnatic hater will simply refuse to agree that it was a major. I personally, do not care and will continue to call it a major. bcoz there isn't much of a difference between lock in and masters besides the no lower bracket, which btw makes it even harder to win. You basically have to go undefeated. And even if there were a lower bracket, let's not pretend Fnatic wouldn't have won it anyways.