The headline, which I do not blame on the article's author, overstates the case.
The tests establish that the marble of the inscription came from the Greek island of Kos, not from Nazareth. This fails to support the claim that the inscription was produced (on imported stone) and displayed in Nazareth.
But that claim itself is tenuous. It is based on a brief provenance note left by a collector in 1925. In fact it's possible that the inscription is a nineteenth-century forgery. And even if it is genuine and it came from Nazareth, the idea that it reflects a knowledge of Jesus' empty tomb is speculative.
This is a very good article that sums up the latest on the Nazareth Inscription. Background here and links (cf. here).
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