When fact and speculation become confused

Often researchers have speculated about events which they did not have direct evidence for. Sometimes these specualtions become more than that, and are later represented as fact by others. This often involves a misreading of notes left by previous researchers failing to notice qualifying statements, such as approximately or circa. I've been researching the Archibald Fisher family. As I search the internet I am finding the year 1767 as the year of their immigration to this county. This was copied from a book. Whoever copied it missed the fact that it actually says immigrated before 1767. It's easy to miss that, but important to read through these entries in books etc. to make sure there are no qualifications. I had to go back to the book to verify what it said. I was getting confused and thinking maybe they did immigrate in 1767. Looking at some of the other records for Augusta County, VA it seems that a lawsuit involving Archibald Fisher and his wife Susanna Shaddon was filed in 1766. So it seems Archibald may have been in Augusta County in 1766?
We do not know where his children were born and most may have been born in the US (speculation)? I am also speculating that it is possible that Catherine Fisher may be a daughter of  Archibald and Susanna? I base this on the fact that it's likely Catherine's husband, Hugh Forgey, was born in around 1766. We don't know how many times Archibald was married. According to a Randolph County History Archibald came from Scotland and first settled in South Carolina?

 Here is what we know for certain about Archibald Fisher.

1. We know he married Susannah Shaddon sometime after November 1765 when she was appointed administratrix for her late husband ( it looks like Archibald and Susanna were married before 9 August 1766 when they filed a suit together?)
2. We know he purchased land in Augusta County, VA on 5 March 1767 
3. Sells his land in Augusta County on 9 Dec 1777
4. We know he was in Sullivan County, TN in 1777 when he signed Holston Men Petition.
5. We know he received a patent for land in Sullivan County, TN (later part of Hawkins County) on 10 November 1784 
6. We know he sold his Hawkins County land on 27 May 1789
7. We know he married Elizabeth Sharp on 11 December 1797 in Knox County, Tennessee
8. He died 1 May 1805 in Ellis Grove, Randolph County, Illinois

We also know the names of his children because they are named in his will.

What we don't know is when he came to America? Did he settle in South Carolina first? Where was his property in Knox County, TN? When did he sell it? Most importantly, what was Catherine's mother's name?