James K. Polk Millican & Sarah Agee Marriage Dillemma?

I'm working on sorting out whether or not there was another Sarah Agee from Yamhill, Oregon who married a Benjamin Coats, or if in fact she did marry James K. Polk Millican in 1866.  I'm seeing this in www.findagrave.com as well as a bit on ancestry, but my research is outlined a bit in this letter I sent to the findagrave contributor for Sarah Coats - daughter of Isaac Agee: 


I have a question and I'm hoping you might have the research to help me "put this to rest."

I was wondering if you have info that would help me determine whether what I'm looking at is correct or if something's remiss - if there's more than one Sarah Agee from Oregon or whatnot?  I'm still exploring it but thought if I asked someone who might have info I might be able to speed up the process. 

Thanks in advance - sorry if this is confusing, I tried to be as clear as possible.

I do have Isaac Agee (1811-1900, b. Tennessee, d. Oregon) on the 1860 and 1870 censuses out here in Oregon (12 August 1870, Sheridan, Yamhill, Oregon & 6 August 1860, Willamette, Yamhill, Oregon) with a Sarah Agee on the 1860 census being listed as 12 years old in 1860 which would put her as being born probably in 1848 (as the census was taken in August, we're at ~8/12 of the way through the year unless the person answering the door was young and didn't give the right date or the census taker didn't write it down right yadda yadda).

Sarah would have been born in Missouri as Isaac didn't come to Oregon until 1852.  This shows on the 1880 census and the 1860 census.

I have a Sarah Agee and James K. Polk Millican being married in 1866 as listed in the Oregon state Archives as being married in Yamhill, Oregon.   

 I do have an 1870 census for James and Sarah Millican up in Yakima but which lists Sarah as being born in Oregon - typical for a census mistake - but also lending credence in my mind that that is where they were from before moving to Washington and that I'm looking at the right couple.

I then have a James Millican and Sarah Millican (Agee) residing in Yakima, Washington on the 1880 census, also with her birth place being in Missouri, and James being born in Missouri too, which would be correct because the Millicans didn't arrive in Oregon until 1843, coming from Georgia, they would have been in Missouri in 1843 to hit the Oregon Trail and been in Oregon as well both that year.

Yet I'm seeing a marriage of a Sarah Agee, daughter of Isaac, to a Benjamin Coates floating around on findagrave. 

Thanks again, sorry for any confusion.