回複：請教:I-130被批準，但不能在美境內調整生份，要等NVC

It's because the priority date is not current. So the beneficiary cannot file I-485 at this time.

"1) in what situation is it possible to be determinded "not eligible"?
You spouse has to keep his/her independent non-immigrant status all the time until PD is up, otherwise he/she won't be eligible for AOS even when PD is current (unless you will get US citizen at that time so your spouse can switch eligiblity category that is allowed to adjust even without a legal status)