I know from historical accounts that Indians in my area did grow corn. A white woman, captured by Indians in Virgina in 1755 and brought to this immediate area described the most beautiful river she had ever seen, the Ohio, and the largest corn fields she had ever seen, growing in the valley beside it.
I wonder though if the pestles I have were used for grinding, due to the size it would have taken a very long time to grind more than a tiny amount. I wonder if instead they were used to crack hickory and walnuts, I've used them for that myself and they work great for it. I've also never seen anything indicating Indians here used corn in a similar way as they did in the southwest. I've heard of a dish made of dry corn and beans, but nothing made from ground corn flour.
I also don't know how long ago corn was introduced here, and the archeologists say 95% of my relic collection is more than 2000 years old. Two places where I used to hunt account for all of my pieces less than 2000 years old. They are actual arrowheads, small, triangular and very finely worked. Pottery fragments, and bone tool fragments are found with the newer arrow points but the grinding stones, if that's what they are, came from spots where the other relics are closer to 5000 years old.
I think it may be a false assumption that Indians east of the Mississippi and especially north of the Ohio used corn in the same ways as those in the southwest and Mexico.