In this scenario, the 4th son was given the name of his father John. John Jr.'s mother is a second wife and her name is unlisted and, even more oddly, is that her second son by John Sr. is named John instead of the first.
In our modern era, I thought the eldest is named after the father (if any sons are). Was this not the tradition in the 1700s? I think the info online must be incorrect and, indeed, the info on other sites also seems incorrect in an even more bizarre, illogical way (two sons with name John!).
There are 2+ profiles for him on WikiTree, but one is empty.