ISTR that being the case even when we were in the EEC but before it had become the EU. There were several cases of French customs (possibly others but France is where most G aircraft going abroad went) asking for the documentation and if it wasn't forthcoming demanding the VAT. I think these were mostly sorted out but there was a lot of bureaucracy involved. I know with more certainty about what happened with UK film and TV crews going abroad. Until about the early 1990s, so before the single market kicked in, they had to have carnets with absolutely every piece of equipment listed and these were quite often checked by French customs. If they'd actually lost something like a film magazine they'd not only have to replace it but would probably have to pay the VAT on it as well on the grounds that they might have sold it there. The main problem was that they were often held up for ages at the ports while all their equipment was checked against the carnet.