Since you mention land records regarding John Taylor, you may have already looked for the same regarding William Nelson."Republic of Texas: Poll Lists for 1846", compiled by Marion Day Mullins lists:
Nelson, William -- Colorado Co. Nelson, Wllliam S. -- Panola Co.
There are people who respond on this forum who have publications on early settlers and pioneers of TX.I would post a query with something in the subject box that might catch their eye "Early TX Pioneers and Settlers".
Forgive me if I make some suggestions you've already tried, but have you checked Upshur Co, TX GenWeb site.Some GenWeb counties are not only putting their cemeteries online, but some other records, too.It would be nice if you could find an obit for Betsey.I would post your query, plus ask if anyone has a county history and would they check for any possible info on your Nelson and Taylor families.
You might try and find a county history for Nacogdoches Co, TX, too.You just never know what might pop up in an old history, or even one of those newer types, where people submit their family bios.
There is a very brief bio on John D. Taylor of Austin's original 300, in the Handbook of TX Online.Maybe the mixup with your John R. came from those early records.You might want to check it out, sometimes it helps to know who might get mixed up with your own family, just to keep records straight. http://www.tsha.utexas.edu/handbook/online/index.new.htmlhttp://www.tsha.utexas.edu/handbook/online/index.new.html