We have an IDIQ prime contract with DoD that has options every two years in March. The contract is SCA covered; we received updated wage determinations via a contract modification from the contracting officer in September 2016; however, the WD was effective in April 2016. My experience has been that the WD is effective when it is incorporated into the contract (in this case September 2016), and that we do not have to go all the way back to April 2016 and retroactively adjust salaries. Is this a correct understanding? Or do we have to go back to April and adjust all affected salaries even though the updated WD was not incorporated into our contract? Is there any law or FAR clause that someone can point me to that states we have to follow the WD once it is incorporated into the contract?