can you have 2 171H approvals?

Okay- not sure if I worded the title correctly. Our 171H expires in early August, we were approved for two and 1 child has come home, but we are nearing the #1 spot for referral soon for 2nd child (VN) -We are concerned that our I-600 may not be filed by the time our current 171H expires. We also may go for another adoption- so we are thinking of filing another I-600A . IF we do this, does this cancel out our current 171H- Or is it possible to have two at the same time ( I know you can have two approvals for different countries- but not sure if it is the same country?) I hope this makes sense. Thanks so much for anyone who can shed some light. MLRJ