[eggsontoast]

I seem to recall LNN TX was shadowing ITV for weeks before going on-air. The stability of the commercial LMS system was hugely important to Carlton/LWT and eventually was running at 99.9% performance.
LNN News did a far bit of shadowing but not everyday and often bulletins on some days and hour long shows another. The first few days of 1993 LNN actually transmitted LWT News branded bulletins. The launch of London Tonight brand was saved until Monday January 4th.
GMTV did a neat thing with distribution to the regions having "PresFax" type running orders showing timings to opt-out from NewsStar, but also Talkback in NICAM so the regions could all hear the St5 production talkback about late changes.