@Saloma:
I'll show you what I mean.
1.) Who gave him the title "World's Strongest Man"? - Someone would have to be the one who started calling him that, how do we know this person wasn't misinformed?
2.) What determines strength? - Time and time again One Piece has showed that the strongest person doesn't always win. What do they mean by "strongest"? Is it being able to lift a lot? Is it fighting ability? They haven't gone into this at all, so you can't use it anyway you like.
3.) What about unknown people not included? - The government didn't even know about Blackbeard, who is obviously a serious threat to him. He was good at hiding despite the fact that he's strong. There's also people like Luffy, who are underestimated and thought to be weaklings.
4.) How long has Whitebeard had this title? - One would think he got it when Gold Roger died, which is probably the case, but if that's true, how do we know he's still as strong as he was? Since we don't know, we also do not know how strong he is.
5.) How strong is "World's Strongest"? - Calling someone "World's Strongest" says nothing about HOW strong he is. For all we know, he's %0.0001 stronger than Shanks, but is the world's strongest because of that tiny difference. You can't use the arguement "He's the world's strongest!" because we don't know how strong that is.
I could go on, but that covers most of it.
Who gave him the title "World's Strongest Man"? Oda did, through several times through different characters. Being stated in the manga makes it canon. Whether it may hold true or not, or whether or not Oda is planning to change this fact in the near future, has no relevance to my argument whatsoever. Actually, I'm not trying to make an argument. I am simply stating what has I have read in the manga and what has been stated. I could care less whether Blackbeard would win right now or not. Because the fact is, they're not FIGHTING right now, are they?
What determines strength? Who knows? Better yet, who cares? This question has, yet again, no relevance to my "argument". But if I were forced to answer this question…. If I remember correctly, it was also stated previously in the manga that Whitebeard is currently the man most likely to become Pirate King. Unless my memory is making this up (which COULD actually be the case XD), that is what I would say is meant by him being the "strongest". Yes, I know my answer doesn't really make sense. Again, I am just stating things that have been said in the manga. However... that was said a pretty long time ago, so it may hold no meaning anymore. We'll see, I guess.
What about unknown people not included? Once again, not a part of my point. Barring speculations such as these, I will take what has been stated in the manga as fact. Once I see someone beat Whitebeard, then that "unknown person" will be strongest according to canon.
How long has Whitebeard had this title? More importantly, how many OTHER people have gained this title after Whitebeard did? Zero. Most of your other points hold validity, but this one is kind of pointless.
"How strong is "World's Strongest"? - Calling someone "World's Strongest" says nothing about HOW strong he is. For all we know, he's %0.0001 stronger than Shanks, but is the world's strongest because of that tiny difference. You can't use the arguement "He's the world's strongest!" because we don't know how strong that is."
….Wtf? Who cares HOW much stronger he is? So what if he is 0.0001% stronger? That's like saying being 30 seconds late is still being on time. 30 seconds may seem like nothing, but it's still not on time, is it?
ANYWAY, my end point is, barring all speculation and what may be changed soon and other people's opinions, the LAST character in the manga to have been titled "the strongest man in the world" is Whitebeard. Regardless of recent events that may change this, or how questionable this statement is, I still see it has canon and I PERSONALLY will maintain this fact. Hell, if you wanna know the truth, I can see Blackbeard beating him. But he hasn't yet, has he? So my view stands true in my eyes.
Okay I think I'm done. :P