Depending on the value, Truth in Negotiations should be a factor. Should a Certificate of Current Cost and Pricing Data be required, there is a requirement for Accurate, Complete and Current data. Therefore, one would need to look at that issue, in light of the fact that this is a sole source procurement.
Whatever the reason for the submission at that point, the impact on the baseline proposal should be reviewed by the cost/price analyst, and possibly by the auditor if the changed rates were previously audited (e.g., indirect rates). The results, once analyzed, should go into an updated negotiation objective prior to negotiation of cost/price elements of the total proposal.