One of the problems we had was that the AS355F1 (IFR) had numerous "CAA" modifications on it from new at the Aerospatiale disptributors Mcalpine Helicopters.
Mods such as 3 axis coupled autopilot, large instrument panel, Radar, radio fits and other modifications, which was a major headache as the modification paperwork from 1985 was not available anymore, and not in the records apart from a few lines of entries in the log books.
That was 15 years ago now, before EASA started, heaven knows how we would get round it now.