
WSM and WSS are not titles, they are statements
When a character is presented they usually have this on their presentation cards:
- Name
- Title
We can see it when Roger was presented as:
- Name: Gold Roger
- Title: "King of the Pirates"
We know is a title when the phrase is in quotation marks.
Like "Garp the Fist" or "King of the Beasts"
That is the title that the in world people called them, in Mihawk's case is "Hawk-Eyes Mihawk". that is his title, because is in quotation marks.
When we take a look at the "titles" of WSM and WSS they are not in quotation marks, they are a direct statement from the narrator, so WB is the WSM just as he is Edward Newgate, like presented.
So no, people don't call Edward "The World's Strongest Man" Newgate, they call him Edward "Whitebeard" Newgate.