Changes are not made without engr. approval.
Not necessarily true. In this case, the design engineers were NOT consulted. You can't trust a contractor any more than you can trust anyone else.
We're all trusting that our hitch designers are doing it right. But you never know. And you never know if the welder putting it together didn't get distracted and end up with a void in his weld, that cracks just as you go over that rough railroad track. Your also trusting that the bike rack is adequate. Same design and construction issues apply.
"You pays your money and you takes your chances!"