Andy is correct in his belief that you have no right to review a credit report for this purpose.
I would strongly recommend reporting the inaccuracy to both the credit reporting agency and to your customer.
I appreciate that your customer is unlikely to be overjoyed by this news but he/she will at least (and I hope with your support) have an opportunity to do something about this at a point when -hopefully- the problem is not time critical.
If your customer first finds out about this when they want to move home, for instance, and your inaccurate reporting leaves them disadvantaged and they find that actually you knew of the problem months or even years before they are going to be very disgruntled and rightly so. In addition by promptly notifying them of the problem you can at least show that you monitor your systems for error and not just leave this as an oversight which happens - however much later- to have corrected itself.
Unpleasant as the prospect might be pick up the phone and call your client.
Matthew
Compliance Officers Association, Privacy Officers Association, AACFE, MICM, SHRM.