Yes, we have very similar issues with development timelines. We work in a large dev team who are simultaneously implementing a front end and re-platforming to Adobe Experience Manager. The complexities involved with their development timelines, and similar politics to what you speak of, protract the release cycle well beyond our sprint cycles. So yeah, there’s a huge gap between vetted prototypes and sandboxed dev.
Probably similar to your team, this requires lots of shoulder-checking when the work goes live to make sure our concepts live through the build. There’s probably something to be said for good documentation (I know that’s not lean, but we can’t all live in an Eric Reis wonderland), and we do rely on that sometimes.
All in all there are struggles with getting good UCD live, but the benefits to the process probably save our ass many times over and create an excellent backlog of design debt when we can’t’ get it perfect the first time.