Ground equipment hitting aircraft happens quite often and unfortunately is not reported on many occations.
It would be nice to think that all the people working near aircraft were highly trained and responsible people,who would report any incidents, but the reality is that if you pay peanuts, you get monkeys. Also if someone is likley to loose their job then a cover up is going to happen.
The worst case I've seen is of a Viscount aileron being bent when hit by a belt loader. The loaders involved only came and told the line maintenance guys (me) after it had taken off. Fortunately it arrived safely.
So Boeing had better make sure that when the structure is hit and no mark is left, the residual strength is going to last until the deepest NDT inspection has taken place.
I imagine that all the design and testing has taken this into account, but the fail safe structure of the 707 horizontal stabilizer was supposed to take care of all damage between inspection intervals. A Dan-Air cargo crew found out that this system is not infalible and paid with their lives.
Further, when doing a walk round, if there is a crack in the paint, then if the aircraft is fairly new I suppose you would assume something has happened. But what happens on an older aircraft when the paint is tired and starting to crack of its own accord. How do you know what the cause is?
I think there will be a lot to learn about these primary structures when they get on the line.
Safe flying.