Loki's bounty is probably special because Shamrock asked the Gorosei to consider pardoning him for his crimes and make him a knight of God. Shamrock was a kid when Harald was a HK and probably saw how powerful he was and how he did a lot of missions for the WG, and he wanted to get another powerful ancient Giant in, and he noticed the WG was losing it's connection to pirates after the warlord system was ended at that reverie. If you remember, Sommers asked Shamrock if he was at Elbaf to visit Haralds grave, so he probably respected him in some ways.
Tbh, I was being kind of dumb to think that Shanks or Shamrock would have went to warn the Gorosei about Blackbeard, since he's one of the most open threats in piracy, bro gave the speech himself at MF lol.