The following is based on readily available online records for the Albemarle, Augusta, and Bedford County areas, as pointed to in the "Related" section above. While records for Augusta are voluminous, the online records for Albemarle and Bedford seem quite limited. Additional records for these areas are available in microfilm format, and a thorough search of those sources may yield better insight into the problems discussed below. Note that while the following discussion uses the "Cowan" spelling of the surname, the "Cowen", "Cowon", and "Cowin" have also been searched in those online sources immediately available.
Sometime during the early 18th century members of the Woods, Campbell, and Wallace families settled in Lancaster PA and/or nearby Chester County PA, and Cecil County PA. They intermarried with each other extensively, with some of those intermarriages apparently occuring in Ireland prior to immigration. Eventually some members of this extended family moved westward into what is now Cumberland County. Along the way, other families also intermarried with them, including members of the Cowan's and Gass lines.
About 1733/1734 a group of these families, nominally headed by person:Michael Woods (1), began to move south into the Shannandoah Valley of Virginia. Some settled on Beverley's Manor near Staunton, and are well represented in Augusta County records. The first Cowan records in this area date to 1741 when some of their children are baptized by the Reverend John Craig beginning in 1741. They were may have been in the area before this date, but their presence earlier than 1741 has not been documented.
Another group, nominally headed by Michael Woods (1), moved east through Woods Gap, to settled on the eastern slopes of the Blue Ridge, between Woods and Rockfish Gap, in what is now Albemarle and Bedford Counties. While we have some records for them, online sources for this area are decidedly less abundant compared to the record availability for Augusta County. 
The first record that we have currently available for a Cowan in this area is a 1745 road order. This order covers a section of Three Notch'd Road from the DS Tree to Woods Gap on the Blue Ridge. Among the members of the road crew are many related to Michael Cowan (1), and other members of his extended family. This is probably a reasonably complete listing of the able bodied adult men in the area. Among them is Person:John Cowan (65). No other Cowan's are listed, and it seems likely that there are no other adult male Cowans in the area.
The next Cowan record in the area comes in 1756 when John Cowan (presumably John Cowan (65)) secures a 268 acres land grant in the Meachum River watershed. Two years later, in 1758, an Eleanor Cowan sells a small (68 acre) parcel of land. In this sale a David Cowan gives up his rights to this property. This looks very much like a transaction related to an estate. Most likely the parcel passed to Eleanor and David as an inheritance. Since Eleanor and David are the first additional Cowan's to be mentioned in the area, other than John, it would seem that John died between 1756 and 1758, leaving this parcel to Eleanor and David. While records for the area are limited, an index of area wills does exist for this period. It includes no Cowan's named John or otherwise. We are left to presume that John (65) died intestate. While it is possible that both Eleanor and David are his children, it seems more likely that Eleanor is his wife, and David is his son. This seems to be made more likely by the fact that David is known to have had a first born daughter "Eleanor", plausibly named after his mother.
A 1759 land sale seems to make the case more solid. In that year David sells a 268 acre parcel to a "John Cowan". This is presumably the same 268 acre tract that John (65) acquired a few years previously.
19 May 1759 DAVID COWAN & wife JANE, planter, to JNO. COWAN for L10, 268 acres Mitchum River adj. HENRY CARR, WM. WALLACE. Wit: JOHN ANDERSON, JAS. COWAN, NICHL. WALLACE.
It is very difficult to interpret these data in anyway other than that David is the son of John (65), and the son of Eleanor. On the otherhand, this is still a circumstantial test, and its possible that other relationships are involved here. Examining the additional data that is available on microfilm, but largely unavailable online, might well provide confirmation, or refutation of this view.