Hi, First, you need to check only release cost estimate (status:FR, costing version: 1) in KEKO - you will not have multiple released cost for the same period of time frame. you can directly check in the material master.
In this instance if you have a released standards from 4/11/2016 to 12/31/2016 (I guess that is only one released-FR), you can post small quantity of production (GR) with the posting date after 4/11 and redo the variance calculation- KKS2- that will update your targets with the April standard cost. Hope this helps, Thank you!!
Regards,
Srinath