I used an e-cert once, and then the refare vouchers on the same PNR just a few months ago. I had to call UA and use the E-Cert, explaining to them that I needed to ticket at ORD. I then went down to ORD and had it ticketed using the refare vouchers. Took a while for UA to figure things out at ORD, and I ended up with a voucher in the end from applying the wrong refare, but it was worth it in the end. Good Luck.