I understand the technical issues, but I want to understand why non-standard fields cannot be used. It does get the job done, just not with other vendors.
So at the end of the day, if I told you I could pass elements such as NOA,BCI,GNO etc… but only to and from elements from a single vendor would this allay your fears.
Please dont take this the wrong way. I am just trying to understand the point you are trying to make.