In chapter 907, Shanks met the Gorosei to talk to them about “a certain pirate”. I’m pretty sure Shanks told the Gorosei about Blackbeard and his lineage. He’s always been wary of Blackbeard from the start and the World government never gave Blackbeard much attention, but now they do.

Blackbeard started with a 0 bounty, which is crazy considering that he was a Whitebeard Pirate for multiple decades. He rose the ranks shrewdly and with efficient brutality and shot to the top. From wanting to turn in Luffy, defeating Ace, earning his Shichibukai position, breaking into Impel Down, releasing some of the world’s worst criminals, killing Whitebeard, and becoming an Emperor.

The World government and the Gorosei treated him like a powerful pirate not really separate from the other Ds, they didn’t give him special treatment like they do Doflamingo. Now, they explicitly recognize his unique lineage. Similar to how they viewed Luffy totally differently after Wano, they always kept an eye on him but they never acknowledged him like they did after Wano, because they didn’t take him seriously enough.

I think they viewed Blackbeard similarly and their turning point was the Reverie. They never treated him differently based on his unique lineage, they always acknowledged him based on his pirating accomplishments (defeating a Yonko Commander as a nobody, recruiting level 6 prisoners and a former Impel Down Jailer, killing Whitebeard and occupying his territories, having two Devil Fruits). Now it seems they are paying to more attention to him and his unique lineage.

But Shanks has both had experience with Blackbeard and warned others about him, namely Whitebeard. Even before Blackbeard was an apparent threat to the pirate world or the World government, Shanks was already wary of him. So I think it makes sense that Shanks was warning the Gorosei about the Blackbeard when he spoke to them at the Reverie.

I also believe that what Shanks has been doing all these years is keeping things stable and ready for someone like Luffy to come. He had an idea of the timeframe but not the details of who it will be or how they would present themselves when the Roger Pirates disbanded, so his pirating activities were mostly to keep the government from consolidating their efforts and disrupting the obstacle course that the Roger pirates set up for Joyboy to reemerge out of.