quick question: if you need another extension while your case is pending, you make infopass appointment right? do they give you another receipt like the I-797c or they stamped it say on your passport? what if you don't have a current passport at that time?

I-751s are regularly adjudicated within the 12 month NOA extension period now.
If you should find yourself in need of a stamp, and you have no passport, the remedy I've read about is that the officer will stamp an I-94 in lieu of a passport.