The inscriptions you refer to aren't Sanskrit, but Hurrian. The inscriptions in question contain Indo-European loan words and seemingly reference Vedic gods, but that does not make them Sanskrit inscriptions. If you're looking for the earliest Sanskrit inscriptions, you're looking to the first century BCE, over a millennium and a half later than this plaque. We have Sanskrit texts that are older than this, but the physical artifacts are newer copies of older copies that don't survive.