OK so I actually looked at the records and did some digging - a lot of inconsistent and conflicting information- hope I have encompassed enough for someone else to evaluate :)
My first comment is that Bryan 331, 746 and 981 are all clearly based on the same information. All have the husband Forbes/Forbis All born in Virginia both profiles that give a date of birth give 1731 and specify Shenandoah, Winchester.
Bryan-83 has a different place of birth, a different spouse, and has a death of 1742 which if they were the person born in 1731 would have made them 11, an unlikely age to be married, let alone married twice.
In one account (Link 1) Morgan Bryan (the 2nd) and Martha Strode had children Joseph, Samuel, James, John, Morgan, William, Thomas, and Rebecca. No Mary, except William's wife Mary BOONE(married in 1755), This account gives Morgan Bryan as the son of Francis Bryan.
In a different account (Link 2) Morgan Bryan is the son of an Unknown Bryan (author believes William) and Sarah Bringer (vice Brinker) In this account Morgan's children are Joseph, Samuel, James, Morgan, John, Elinor, Mary, William, Thomas, Sarah, Rebecca; the first four or five being born in Chester, PA before they removed to the area later known as Winchester in 1730. Mary was, by this account, not born in PA - the records, except Bryan-83 make sense with the family settling on Opequan River.
According to (Link 1) the Bryan family less son Joseph removed to Davie or Rowan, NC in 1748 (except son Joseph who remained in VA) which is where daughter Rebecca married the famous frontiersman Daniel Boone in 1755.
I would tend to give credence to Link 2, simply as it is written by a great-grand-nephew of Mary Bryan, unfortunately he says nothing further of her than listing her as a child of Morgan Sr.
Another reference (Link 3) also lists Mary but gives no further information. This work appears to be the best researched of the documents examined. Interestingly this reference suggests that Martha Bryan married first Stephen Gamo, and Second ? Fobes/Forbis of Kentucky.
This page (Link 4) is about the Forbis family that lived in Virginia, North Caroline at Rowan and Bryan's station, and then into Green, Kentucky which largely mirrors the migration of the Bryan family. Footnote 1 mentions a Mary Bryan, but this is probably Mary (Forbis) Bryan wife of Morgan Bryan Jr.
The account of descendant George Bryan published in 1927 (link 5) supports the other references that the families most intertwined with the Bryan Family are Boone and Forbis (also given as Forbush) so I would suggest that the unknown husband should be a Forbis and not a Forbes
A final discussion (Link 6) helps put, in my mind, a plausible scenario: Mary , daughter of Morgan and Martha Bryan is, according to Link 3, third in Birth order and is therefore born before 1830 in Chester, PA if Link 2 is correct that the first 4 or 5 children were born prior to removing to VA. The 1742 will of Mary Curtis discussed at Link 6 is persuasively the correct Mary Bryan simply based on the names of all the male family members (given in Link 2/3) as well as sister Ellinor. Since Thomas Curtis passed in 1741, their daugher Mary Curtis (b.~1741) would have been taken in by one of the other family members (possibly appearing in some records as Mary Bryan as a consequence) There could also be an error wherein people have associated Mary (Bryan) Curtis as the person who marries ? Forbis, when it is Mary Curtis (d/o Thomas Curtis and Mary Bryan) who did so.
Link 1. http://archive.org/stream/shearerakersfami00shea#page/10/mode/2up
Link 2. http://archive.org/stream/boonebryanhistor00brya#page/12/mode/2up
Link 3: http://archive.org/stream/boonefamilygenea1922spra#page/508/mode/2up
Link 4: http://alvispat.wordpress.com/forbis-james-sr-of-rowan-co-nc-bryans-station-lincoln-and-green-counties-kentucky/
Link 5: http://www.gabrielferrel.citymax.com/f/GeorgeBryan_recollections.pdf
Link 6: http://wc.rootsweb.ancestry.com/cgi-bin/igm.cgi?op=GET&db=frostinaz01&id=I9836