Since f2a visa is current, does nvc assign interview date based on your priority date or case completion date?

What if pd oct. 2011 got case completed on oct. 20 and pd may 2012 got case completed on sept. 20 who gets interview letter first provided f2a visa is limited..

Thank you![biggrin]

It depends on which I-130 is approved first. It is typically sent to NVC as soon as it is approved. Though it can sometimes take 4-8 weeks for USCIS to send it to NVC. Please see the blog post below for steps and various timeline at NVC:

http://blog.mygcvisa.com/2013/09/nvc-consular-processing-steps.html

Interview is typically based on case completion date. There are also other factors involved such as visa availability, interview slots available, background checks, fees and forms payment, etc. The link above should explain the complete steps for NVC.