Here's information gathered by a deceased relative.I can't vouch for it's accuracy but I think it's reasonably good.
Robart Knowles received a land grant on "Brown's Sawmill Creek" in Bladen county about 1736/37.By 1744, Robart Knowles was living in New Hanover County, being listed on a "corn tax" document.I believe that the area of what was then New Hanover county became part of Duplin county in 1749 when Duplin was formed from New Hanover.
Robart Knowles died in 1762 and left a will in Duplin county NC.Unfortunately, it has become tattered and torn over the years.It is possible to read what appear to be parts of several girls' names, plus the names Robart, James, John and a torn-off entry that appears to read "--lomon" which some people have guessed may be "Solomon".
Robert (note more usual spelling) and John Knowles enlisted in the Duplin county militia in the Revolutionary war.They were at the battle of Rockfish Creek (near Wallace NC, on the present day border between Duplin and Pender county).John Knowles was wounded in that battle and left disabled for life; he received a veterans pension.
John Knowles and Robert Knowles are both listed (apparently near each other if the numerical listing is any guide) in the Sampson county census of 1790 (Sampson was created out of Duplin county in 1789).The category for them in the census shows both as heads of household and "male - over the age of 55".Robert listed as birthplace "Scotland" and there is no entry under birthplace for John.
Robert Knowles died in 1792 and his will is recorded in either Duplin or Sampson county, NC.John Knowles died in 1804 and his will also exists.I am descended from John Knowles.
I think that there are three likely scenarios:
1)Robart Knowles and unrelated persons also named Knowles settled in Bladen county in the 1700's.Robart Knowles moved on to Duplin County and the unrelated Knowles persons stayed in Bladen.
2)Robart Knowles and relatives (but not children) also named Knowles settled in Bladen and Robart moved to Duplin, leaving the other Knowles persons in Bladen.
3)Robart Knowles settled his family with some children born in Scotland in Bladen in the 1730's.He may have had more children born in North Carolina after they settled here.Robart moved to what is now Duplin or Sampson county within a few years, but some of his children (perhaps older ones) remained in Bladen and inherited some to the land that was originally granted to Robart Knowles.If this proves to be true, the Knowles lines in Bladen and Duplin/Sampson in the 1800's were related but were diverging into distant relationships.
It is only a guess on my part, but I would guess that scenario 3 is most likely to be correct.Note that the first names in the Bladen records are similar to the names in the Duplin/Sampson families.