I agree with you that sources should be better identified. I have been trying to sort out the references for Harrison-889 and found the following information:
* Surry County records; Sussex, A Tale of Three Centuries is available online here: https://archive.org/details/sussexcountytale00virg
There is a little information regarding a Captain John Mason (there have been many of them) but I did not find any references to Elizabeth Harrison.
*I have not been able to find an online resource for "Virginia Magazine of History & Biography Vols 200, 29, 34" (Not sure that there are actually 200 volumes, so 200 may be a typo)
*Information from Application for Membership in the Daughters of the American Revolution, D.A.R., approved March 20, 1963 for Frances Ellen Walk, cites "Magazine of History and Biography, Religns of Rives: Masons of South Side Virginia, p. 3" as source for Elizabeth Harrison as wife of Captain John Mason, son of Major John Mason, on whose Revolutionary War Service DAR approval was granted. See image on her son's profile here: http://www.wikitree.com/photo/jpg/Mason-3332