Re: Customer Rejects our CAR
...Ambiguity predetermines that tasks cannot be defined precisely, and that interdependencies between tasks are unknown.
To say that we have clearly demonstrated a thorough knowledge and understanding of your labeling requirements in the past and therefore dismiss the human factors caused by ambiguous practices, I feel is a mistake. These tasks not being clearly defined is a contributing factor....
But saying that and keeping my job would be mutually exclusive events!!!
As others have said, you can be entirely right, but (assuming you want to keep this customer) it's almost certainly not a good idea to say so to the customer. And as others have also said, if it was a contributing cause, it would have been wiser to have attempted to fix the unclear specs earlier on, ie, before something went wrong. (I could quote you clause number on where it says so, but won't.)
Otherwise, looking at it from the customer angle, it could look as though everything was fine until the error cropped up, at which point you (at least partially) blamed
them for the error.
But look, 'real world ' issues demand suitable 'real world' solutions. Some suggestions have already been made. If I might add: as a relatively young quality professional, when I was sure/knew I was right, I'd stick to my guns come hell or high water, and refuse to budge. But take it from me as one who knows and learned, often the hard way, it's a behaviour that does not lead to 'win/win' solutions and it definitely does lead to win/lose confrontations. And those generally don't have
effective results - at the very least, they leave people behind with noses out of joint. Now, you might think that might not matter, but often it does.
Ultimately, a result that's effective for everyone involved or with a stake in the issue, is always going to be preferable and a far more positive outcome. Quality people who understand that and can keep their eye on that as well as on the substantive issues and particularly not on the black and white of who's right/wrong will always be more effective in their jobs and more widely valued and respected.