Man I hate that happening lol.
But then I wonder who his parents are because they were never shown or mentioned. Are they people that came over 50 years ago? Descendants of people 50 years ago? A wano person married a neighboring village person?
People mention he may be related to Ryuma but Ryuma was a Shimotsuki and so was Koushiro so he should know if Zoro is a relative plus that would make Zoro and Kuina related which never seemed to be an implication.
Edit** I found it. It was added scenes in episode 19 from chapters 5 and 42. Zoro says he's unrivaled in the village over so it made me assume he had been hopping from village to village.
Chapter 5 only shows after the 2001st loss not the stuff before. Maybe I'm not as crazy as I thought with that Teach scene but still haven't found it yet.
Oda gave a while ago some background information in a SBS segment. Kozaburo was not alone when he left Wano and eventually his group ended up in East Blue where they saved the local populace from a band of bandits. They assimilated with the locals and founded Shimotsuki Village. This is also indirectly confirmed this chapter by the children who say that the village was founded by 'pirates' two generations ago.
Though, it's indeed a bit of a plot hole how Zoro fits in all of this. Most likely a lot of villagers can trace their lineage back to Wano, but it's odd that it has been emphasized so strongly that Zoro looks like a Shimotsuki, yet he has been completely omitted from Kozaburo's line of descendants. I hope Oda will address this at some point, but it's one of those things I can see being left in the open (at least for now).
I mean most likely the majority of the people who left with Kozaburo, were from Ringo and/or his kinsmen, friends, subordinates etc. I don't find it a stretch to think that there was another notable Shimotsuki among them.
With all the focus on Enma and the crash course on Swords 1.1 you might forget that that there was another interesting tidbit mentioned in this chapter:
Why were the marines chasing them? And why did they left Wano in the first place for that matter?
I find it hard to believe that they left Wano just to found a village on the other side of the world. There was a purpose for their journey and along the way it seems they had a showdown with the Marines. This is complete conjecture on my part, but my favorite scenario is that Zoro's hypothetical grandfather was also a Shimotsuki and part of Kozaburo's group, but that he lost his life during a fight with the Marines and they had to flee and abandon their objective.
This ties together with how so many swords from Wano spread across the world: they came along with Kozaburo's group. If most people from the group came from Ringo, they definitely had a sword as it was customary to give each person a sword starting from the day they were born. And in particular the Kitetsu line is interesting as these were all made by Hitetsu. How exactly did Sandai Kitetsu end up in East Blue? I've been saying for years that one of those Five Elders has Shodai Kitetsu in its possession. Imagine that it originally belonged to Zoro's hypothetical grandfather and then lost in a battle. Then you get a parallel with Zoro wielding the "3rd generation Kitetsu" while his grandfather wielded the "1st generation Kitetsu". Though, again this is all complete conjecture from my part.
