I "knew" that William's parents were Thomas Albea and Sarah P/Corley (the name was not clear). A helpful researcher with access to Lincoln County marriage records had given me a marriage date: 10 Sep 1867. A while after that, the GA State Archive began posting scanned marriage records online. These records must be browsed manually, using the original index from the records. Despite these records covering a large date range, I could not find Thomas and Sarah's marriage record. This made me doubt the validity of the date I had been given.
On my last post, a helpful comment pointed out that GA Marriage records were searchable on FamilySearchLabs and that records for both of Thomas' marriage were listed there. Sure enough, I found records for Thomas and Sarah Corley in 1867, as well as for Thomas and his second wife, Susan Pitman, in 1884. But I had not found these records on the indices at the GA State Archive. Turns out that the indices were just missing this information. I had to manually browse through the images, but I finally found the records for both of these marriages (though the one for Thomas and Susan isn't fully filled out). Now with concrete dates, I can be sure to assign Thomas' children to the correct mother.
The research I'd done so far on William and Nellie had also proven that a suspected grave for Thomas was the correct one. I posted the record on FindAGrave.com and requested a volunteer to photograph the grave for me. Thanks to a volunteer, I now have photos of Thomas and Susan's graves.
Because Thomas had been married twice, I wasn't able to confirm that records I was finding of him were actually him. Because the wife's name didn't match the woman I knew to be the mother of my ancestor, I was hindered in my research. By researching all of Thomas' children - and not just my direct ancestor - I have been able to discover the name of the second wife and start breaking down my Albea brick wall. I'll continue to write about this family as soon as my requested documents arrive.