My 03/04 Starts have no expiration, though someone called and they were told 8. This is the first I've ever heard 6. But honestly? I think headwing designs have come a long way lately and I won't keep using mine...I much prefer the wider designs on newer seats (based on various crash test videos I've watched and how they seem to contain heads better--the newest Starts even seem to be considerably redesigned, and not sold here, yet at least).
Our belt guides only seem to work with some seating positions, at some height settings...we've had no end to the frustration of them flipping closed at the wrong time.
Otherwise, we have loved ours, they ARE super super super comfy