Agreed that it would not be likely that the Nancy on the deed was a young girl. It is far more likely that it was the grantor's wife. Even though the dower law was no longer in effect in NC, older couples often still followed that tradition from English common law, particularly if they were from VA. I am not familiar with GA laws during that time period.
I hope your helpers are not being too "20th century" about interpreting the "Jr." in records from the 1800s and earlier. It did not necessarily imply a family relationship, but any family relationship could also be something like uncle/nephew, etc. "Sr" and "Jr" were very fluid and temporary designations in that time period, used by the county clerk to differentiate between two county citizens in the same jurisdiction. "Sr" was simply the elder of the two, and "Jr" was the younger.
Also, let's say there were a father and a son by the same name. If the father died, the son becomes plain Jesse Harris without any "Jr." Nowadays, men often keep that suffix until death. For that reason, I often prefer to use the dates of birth and death in parentheses after a name, as a better way of making it clear which man I'm discussing. I've heard some real tales of woe from a few people after realizing they pursued the wrong family for years before realizing they made that mistake.
I'm sure you've realized that he could have had Nancy sign the Jan 1804 deed, and she could have died soon after, and then he married again in May. It happened. Men wanted company and helpmates, particularly in frontier areas.
And he could have held onto his Rowan land until his son was old enough to work it himself, or for whatever reason he had. I have ancestors who tired of frontier life in NC and retreated back to PA after a spell of some years, so perhaps he wanted to make sure of the relocation before selling his land in Rowan.