Derivative Green card received Primary applicant still pending 3 months later

[shockabsorber7]

My spouse has an employment based green card application filed. Our date became current in December 2013. We filed our I-485 and received our EAD and AP card in January 2014. In March 2014, my actual green card showed up in the mail while my spouse (the primary applicant) is still waiting as of June 2014. When we inquired about the delay with the company lawyer, at first we were told that the primary application was also approved but not updated in the system and to allow USCIS 60 days to issue the card. But now, 60 days later, we are being told that the EB3 ROW dates have retrogressed and  that is why my spouse's card is delayed. 

Isn't my application tied to my spouse's and if so, how did I get my card before my spouse's was even approved? My spouse went to the local USCIS office to inquire further but they didn't seem to know much about what was going on besides what we can see for ourselves on the USCIS Case status website.