after several trials I reached to the solution...
I'm just co-relating words from @CGBenner... "the BOM will reflect whatever the current Model State is in the part or assembly file" & words from @johnsonshiue ... "use Replace Model Reference command (Manage -> Replace Model Reference) to switch to a different Model State"
So, while replacing model reference (through, Manage > Replace Model Reference), Inventor giving you the option of changing part list according to the current model-state. So, here, user must set the expected model-state in ".iam" file & then replace the file reference in ".idw" document.
What I learn here is, If user just change the model state in drawing file by editing views, it will not reflect in part list. User must set the expected model state in ".aim" file & then need to change reference in ".idw" file (through, Manage > Replace Model Reference); which is quite cumbersome task.
I think, Autodesk need to improvise this method in next version by just right clicking on part list & choose the expected model-state, so that, BOM/part list could change within few seconds.