what type of travel vouchers are they? What is the profile name?

If i understand correctly, canceled tickets refunded in the form of a voucher should say Travel Voucher Exchange Coupon and they would be UAL/ Travel Voucher and those are type B certs. To my knowledge, those are combinable.

I have found this to be helpful and could save you anguish-

When booking flights, make a reservation with res and ask them to put your ticket on hold for you to issue at the airport with vouchers. Make sure to give them the profile codes and voucher numbers. There they can look up the profile and see if they are combinable. And then have a service director notate the record in the "United Field" that you are bringing in those vouchers and that them being combinable is authorized and allowed. Then usually ticketing agents would comply cos someone higher up has put their stamp on it.

With CO coming on board, there are a lot of new rules so i am quoting what i know with PMUA.