Hi, Susan....don't know why I just found this. Sorry.
Apparently, Elizabeth Lane Dail died and John Bartlett Dail remarried Sarah Absilla Boyce, by whom he had two more children. So, Elizabeth was the mother of all but the two youngest boys. I think John married Sarah in 1879-80, that's why she is on the 1880 census.
Also, I'm not sure now that Elizabeth Lane was Sarah Elizabeth. I think that may have started before we all realized that she died and may have thought she went by Sarah (as per the 1880 census.) Is this making any sense? Hope so.