JF - I think your point was that these variations, once an aircraft design is basically sorted, are rarely catastrophic. My point was that aircraft do vary in small ways, such as to make standardised performance or (especially) handling data incorrect - and thus degrade, but not catastrophically so, safety.
So, I suspect that we were making different points, and aren't actually disagreeing with each other.
In this harsh commercial world we live in, there is much pressure nowadays not to do the sort of fly-fix-fly work on new-build aeroplanes that you did at Dunsfold. One tries to resist it and get aircraft as standardised as possible, but it can be a battle to be allowed to. Company accountants want to keep the testing down to the actual minimum, and at times these days I think they're actually supported by people at the authority, who rarely see a badly sorted aeroplane and assume that they all come out of the box spot-on.
G