NQSOs are not accorded any tax preferential treatments.  The bargain element will have already been subject to tax in Box 1 of the W-2, which forms the basis.  The custodian broker would have good records of these transaction and could generally be relied upon for the information they provide.

Unless your client feels that the amounts reported on the 1099-B is not correct, you should go with what's reported on the form.  Given the small amount of loss, it's probably a same-day exersale, which was used, at least in part, to fund the exercise.  The difference is probably a combination of transaction costs and small fluctuation in the share price.

Since this is a covered security and the basis is reported to the IRS, it does not need to be reported on F.8949 and can go directly to Sch D (unless there are other adjustments that need to be made for some reason).