I haven't tracked the Stonums through Tennesse, so I don't know where they were during that period.
As for George Norise Stonum's middle name spelling, that is the way it was spelled in legal documents in Richmond County, VA. I have assumed, like you, that it may have been mispelled and that he was named after his grandmother, Susannah Norris. However, I think I should be frank in stating that I can't prove for sure that Susannah's maiden name was Norris. I have strong circumstancial evidence of this, but I can't prove it at this time.
As to George N. Stonum's year of death, I don't have any information on when or where he died. However, I do have a copy of a Power of Attorney from Clinton County, MO, that lists a court appearance dated 6 Mar 1843 in which George N. Stonum appeared in court to testify of his relationship to Susan Sampson (his sister). In the document it states that George N. Stonum is incompetent to care for the estate of his minor son, James Stonum. It doesn't state why he is incompetent though. This is the last record I have regarding George N. Stonum. He would have been about 61 years old at this time. I assume he died between 6 Mar 1843 and 1850, as I have not found him in the 1850 census.