I tried and tried to get two teams who were working on critical-but-independently-developed systems to put together an ICD. Team 2 says "no problem!" and comes

I tried and tried to get two teams who were working on critical-but-independently-developed systems to put together an ICD. Team 2 says "no problem!" and comes back with a document 2 weeks later. Team 1 says "this proposed interface is terrible, here's a much better way to do it". Team 2 replies "oh yeah that's a nice interface but too late the interface in the ICD is the one we built two months ago can't change it now"