“Ussher had little more than the Textus Receptus of the Bible to work with.” Problem is, the Bible texts found more recently make the situation worse.
It seems few people know that many of the disputed the modern renderings are based on the few Alexandrian texts that contradict each other even more than they contradict the Textus Receptus, or that at least one of them the “textual critics” lift up includes the blasphemous Shepherd of Hermas that advocates taking the Mark instead of rejecting it, or that the two most quoted of them were found in the middle of a trash basket waiting to be burned for a millenium, or that another of them was found hidden away in a dark corner of a Vatican basement.
Wherefore by their fruits ye shall know them. Most modern NT’s are based on Greek texts derived from the one Westcott and Hort created from those Alexandrian texts, two men that denied Genesis One, supported Darwinian evolution, scoffed at miracles in the Bible, denied the virgin birth, ridiculed belief in the Resurrection, and said Christ’s expiatory sacrifice was a horrible idea.
Plus the Greek lexicons most modern translations use are based on the work of one Gerard Kittel, the “Christian” spiritual adviser to Adolf Hitler, the infamous character who wanted to abolish both Judaism and Christianity.
The date in Ussher’s writing is too exact for me, but it is very close to other numbers I’ve seen that are based on the genealogies in the Bible. These genealogies are very precise, same as the Creation narrative.