Why do astrologers check both the D1 and D9 charts before confirming a powerful yoga?

A yoga that looks complete in the main birth chart (D1) can still be unconfirmed if the same planets aren't also well-placed in the Navamsha (D9), which reveals a deeper, more refined layer of planetary strength. This is why rare, high-value yogas — like Akhand Samrajya Yoga — are only confirmed after checking both charts together, rather than declaring them from the D1 alone.