Primary green card approved but dependent is still waiting for visa number

My employment-based green card was approved and delivered, but my spouse dependent I-485 is still pending. We both filed years ago, and my spouse also received an RFE recently. Someone mentioned that the dependent may still be waiting for a visa number. How do people usually understand this situation, and is there any way to tell whether the dependent case is stuck at visa number allocation, field office review, or normal processing?