Turns out that the problem was not with the function module RV_BILLING_PRINT_VIEW. It was doing exactly as it was told.
The problem was that there is a function module that gets called afterwards called GET_ZTERM which was customzied. It said that if the description is in english, go into T052U and get the payment terms description from that table. In many of the payment conditions, there is no english translation despite the fact that there was a record in T052U. In the case of the one that was working, it was simply working because there was no T052U english record at all so the conditions were not met in GET_ZTERM so nothing was changed that came out of RV_BILLING_PRINT_VIEW.
On the one that didn't work, it came out of RV_BILLING_PRINT_VIEW just fine but there was a record in T052U. Unfortunately , it was blanks so it was replacing the description from RV_BILLING_PRINT_VIEW with the blank description of T052U.
Thank you all for your help. All is good now.