User blog comment:12th Supernova/Chapter 794: Memory/@comment-183.90.36.142-20150715165609/@comment-10543621-20150716233602

You can still be thankful for someone's who's dead ya know... For past experiences? It's really no different from him being thankful of Luffy considering prior to Alabasta, the only memories Ace had of Luffy would be from their childhood, exactly the same as his memories of Sabo.