No need to read any further than that.
Where I grew up in Western Pennsylvania, "I seen" is a very common speech error which simply results from the language people are raised with. If I discounted everything I heard simply because the speaker started with, "I seen," I would have had to ignore the lessons I learned from a lot of old WWII vets, coal miners, steel workers and a lot of otherwise very intelligent, if undereducated people. Unfortunately the rest of our nation is not like Texas, where no doubt, every person speaks perfect English.
I had a COLLEGE GRADUATE!!! co-worker who constantly used that grammatical monstrosity. I brought him up on it one day at work, and he argued that he was right to use it. I couldn't talk him out of the usage.