I don't know if the rules have changed or not (don't work there any more), but a few years ago at a certain 'Big Airline' you could do a critical task on all 4 engines.
This was once brought up at a safety meeting and the waffle from the front was that it was different to doing it on an ETOPS twin.
It was then pointed out that if it had been done wrong on the first engine, the chances are the next three would be wrong also.
More waffle followed by a change of subject
