Other mistake: Beginning of the movie young Wyatt running through the corn field the rows were straight. I don't think horse and a planter can get them straight.
Suggested correction: This is an assumption, not a mistake.
A planter of that era wouldn't plant rows like that. At the time of that the horse drawn planter would be at best 2 rows per pass and used a trip to drop seed. Nothing like a modern looking planter would produce.