User blog comment:NguyenAnhLam/Vivi 2 years later/@comment-1784001-20170219050616/@comment-24850639-20170220211113

This. Cover stories that aren't "fan requests" are generally considered canon to the story. Most of the time they are things that Oda wants us to follow or note, but not worth serious panel time in a chapter. Stuff like the "From the Decks of The World" mini-series for example are simply meant to remind us of all the people around the world that the StrawHats have relevant connections to, and how those people have been doing since we will probably never visit their location again story-wise. Caribou's story helped highlight Drake's connection to Kaido, while we were at a place in the story where we didn't really understand why it would have been relevant. Even going way back to Buggy's, it helped provide background on his and Alvida's appearances as antagonists in Loguetown. Though the anime still decided to show it, we wouldn't have thought any less of it if they hadn't, as it made perfect since that as pirates they would still have an eventual goal of the Grand Line.