In fact, i had a thoughts that Yamato might be the reason why Kaido want to go to Marineford to save Ace.
And then Shanks stops him.
And then Shanks stops him.
I doubt Yamato even existed as a character 30 chapters ago, let alone in Marineford. Oda didn't even know Kaido's design after Water 7, let alone know about Yamato.