You can call Chicago National Processing Center (312-886-8000).
As I know, even cases they received from 12/2003 to 10/2004 from State Workforce Agency(SWA) have all been transferred to Dallas Backlog Center.
So, if you file RIR or regular LC now, all cases will be forwarded to backlog centers by the SWA and your case will be at the end of the long queue.
However, if you have used more than 4.5 years of your H1B, you may need to file your LC no matter what, so, you may get the chance to file the 7th extension of your H1B.