"What makes no sense to me is that if you can visibly see it how come you cannot find it through assay results."

When they send samples in the be assayed, they first cut the core in half, keep one section, and send the other one off. According to previous posts, the core halves that contain the VG are sometimes kept in the coreshack while they send the VG-less half off for testing. Why they do that...I have no clue.