About the second marriage for Samuel - As you see I noted that I could not verify it (guess you had the same experience). But that was posted here on Genforum (in the Stouffer family forum I think).
On Family Search I found Samuel and Catherine Stouffer in 1850 (I'm going by my memory here, but I think that's what I posted earlier). They were with an infant child named Isaiah - so that fits for "your" Samuel and Catherine (as they later had a child Isaiah, and not uncommonly parents named a child after an earlier child who had died). They were also in the right town and county for "your" couple, and of the right ages! Also I didn't see and alternate Samuel that year who could be "your" Samuel.
You're noticing my point I'm sure - that if Samuel and Catherine are together in 1850, then the "first wife" theory is shot.
So that would be good for you to check on Ancestry.com: To find Samuel and Catherine in that year, and look at the original census record. Also see if you can find more than one Samuel Stouffer/Stauffer/Stofer/Staufer etc. that year - because "your" Samuel has to be someplace with a "Sarah" if the first wife theory is right.
I thought the Genforum poster could be wrong about the "first" wife, but if you are able to contact theh poster, she call tell you what records or evidence she has to substantiate the idea. Otherwise, writing to the county for the birth records for the oldest children (or one of them) would be a way to find their birth mother's name.
You mention "Sarah Catherine" - yes - that is one way people get confused about who is who - if her name is Sarah Catherine and she was called Sarah in one record and Catherine in another but it still could be the same person.
Another thing you can do for your book is say "we don't know for sure." Saying what you don't know can be valuable too.