After going over this chapter again, I got to thinking…
Not only were those from Ohara the only people (in recent times) to be able to read the Poneglyph's, but with them being scattered in obscure places and kept hidden by those that live by them, it certainly validates just how hard it is to reach Raftel.
The Minks have kept this red Poneglyph quite a secret as even Jack did not know to look inside the whale for Raizou. I'm sure very few people, not even Big Mom or Kaidou, are aware of what is written on the Poneglyph's they now have, so they aren't even aware of the significance of the red Poneglyph's and their relation to one another.
Aokiji is a huge X-Factor in all of this in my opinion as he has a high chance of having been privy to the significance of the Poneglyph's since he was an Admiral and part of the force that exterminated the scholar's of Ohara. While I'm certain he can't read the Poneglyph's, even if he knew that the red Poneglyph's point to Raftel or that the Poneglyph's hold the secrets to Raftel, and he divulged these secrets to someone someday - Blackbeard? - then Nico Robin would immediately be hunted down.
I also wonder who is aware of the Wano Poneglyph. It's obvious how the Minks are aware, but I assume they kept it a well hidden secret as Wano was not part of the World Government and implied to be a secluded, secretive nation. After the events on Zou it seems even more apparent that Wano kept the Poneglyph a well guarded secret as not only was Kozuki Oden fully aware of their significance, but died protecting the secrets of his journey with Gol D. Roger to Raftel. The Shogun's death seems to have been fairly recent, and I assume many would have tried to infiltrate Wano if it Oden's relation with Roger or the red Poneglyph were well known.
I guess a big question I'm left with is when did Oden join Roger's crew and how much or how little did the WG know about Oden's affiliation with Roger and journey to Raftel? If Oden joined Roger towards the end of his journey, as part of the final stages to get to Raftel, it's possible not many people knew him as part of Roger's crew and would have been successful in staying hidden all this time... Perhaps Kaidou, or one of his crew, remembered Oden which then led to his death when he wouldn't tell them what they wanted to hear.This is all theory though.
@Long:
Since ace was in wano while on WB's ship, does this mean whitebeard knew about this poneglyph? I mean if it was kaido's territory then i doubt ace just is able to make hat in peace and if he had a relationship with the kouzuki and/or minks he should at least have one,
I think it's safe to assume that the events that took place on Wano, with Kaidou killing Oden, happened fairly recently. And that Ace visited Wano many years ago. It would seem quite odd that Momonosuke and Kin'emon are still fleeing from Kaidou after all this time, and that Raizou chose to flee to Zou with Jack only JUST recently trying to find him there.