When a user navigates to the Item Revision record (Lists> Supply Chain> Item Revisions> click on View for any Item Revision record), there is a field called Effective Date.
1. When a user created or modified an existing Assembly item record to assign to the field Effective BOM Control the value Revision Control, the Default Revision field becomes mandatory. This is a text type field to which one can assign value for the Item Revision name.
2. When the item record is saved, here is what it does:
a. Automatically created an Item Revision record with the Default Revision field value set back in the item record for that assembly item. The default Effective Date set is 1/1/1970.
b. Assigned the said item revision as the Effective Revision of the components of the assembly item.
Further, when the Effective Date in the item revision record is changed, the same date is passed on as the Effective Date of the components back in the item record.