Topic: what is different between "case was approved and case was received at my local office"?

"Case was received" - still at USCIS for review. "Case was approved" - USCIS finished the review, and your file was transferred to NVC, and NVC will issue you a letter with a GUZ number.

Topic: Date of Filling Application Confusion

As others who are currently *legally* staying in the US, your wife could submit Form I-485, to adjust her status, on her PD of "Dates For Filing Applications" (according to her borned country) arrives.