I think there’s an important difference between never being asked at the border for evidence that the child can legally travel abroad, and never asking the other person with parental responsibility, for permission for them to travel, where it is required to do so.
If permission of the other parent is required and it hasn’t been sought, either verbally, or in writing, you could be committing a criminal offence. It’s a bit like saying you’ve always done 50 mph in a 40 mph zone, but you’ve never been asked what your speed was or pulled over by the police.
However, it is of course quite possible that having it in writing might not be required, if the other parent is aware of the travel plans and they are happy with them, and this has been communicated verbally.
The difficulty comes when the child is taken abroad in circumstances when one or more of the above does not apply. You could find yourself in hot water.
It’s a difficult area for separated parents. I am about to embark on the exact same discussion in a few weeks time and I know the other parent is not going to be happy that I am planning a foreign holiday, mainly because they are not in a position to do the same. 🤦♀️🤦♀️
Happy travels! 😊