As we can see, Oda has a fifth unknown man who survived the Rocks incident. This man i Believe of course is dead since there's no sign that he survived past this stage into the Yonkou Era.
Whoever he is, he is greatly irrelevant to the current story, Even more irrelevant than Shiki himself, so I expect the best use he has in the story is Lore for something else.
Here's my theory on who this is. It's a man called Vander Decken.
https://worstgen.alwaysdata.net/for...-the-origin-of-the-davy-back-fight.897/unread
What is you guys' theories on who this is?