Law regarding Interfiling and Priority dates

[nomad1484]

One of my friends encountered an issue and it would be great if one can shed light on whether USCIS interpretation of the interfiling law is applicable or GC was issued in error.

So Case is:

Primary applicant (chargebility India) had EB1A approved with PD in April 2017. Both Primary and dependent spouse filed I-485 in April 2017 and got the EAD/AP and recently in 2018 had the EB-based AOS interview. When I-485 was filed, both their receipt notices carried the PD of April 2017. At the time of interview EB1-India wa snot current, so GC was not approved

The dependent had an approved I-140 (again chargebility is India) from his/her own employer under EB2 category with PD of August 2016.

So at present given moment, both EB1 (PD April 2017) and EB2 (August 2016) for India is also not current

Now after recent visa bulletin, suddenly, they received their I-485 approvals and their GCs. Seems like USCIS applied the interfiling rule by using the Primary's  EB1A I-485 but used the priority date of the dependent spouse's EB2 (even though its not current) to approve the GC.

The GCs carried the following codes. For the Primary EB1 it carries both E16 and E19 codes (so saying primary on EB1 application but dependent beneficiary of spouse's EB2 date) while the spouse's card says only E19 (so dependent of primary EB1).

 

So can the USCIS apply the interfiling rule in this case? Has the firm ever encountered such a case where one just exchanges the PD between spouse's?