I mean, if you want to go there it makes literally no sense for it to be Caribou.

• He gets the information about the weapon in 1056, which also has Luffy getting ready to leave
• Blackbeard would've also had to grab Sabo, who has a lot more presence and shown free as of 1054
• He would've also had to get Vivi at some point despite there probably being increased security following Cobra
• From there, Devon would also need to be sent from somewhere to where-ever Luffy is and run into him in time for Blackbeard to accomplish all of these things
• And even if all these things did happen in the span between them setting sail and then, it's weird that Oda would set up Caribou mentioning ancient weapons when Blackbeard mentions Road Poneglyphs. It's a red herring that adds absolutely nothing for no known reason.