Dear Muhammad,
System will pick up BOM3 from OS32. It will not pick up BOM2. Since you are maintaining 'selection by date', it is controlled by the date validity period.
For example, if you maintain in OS32 that BOM3 is valid, but in CS02, you mark BOM3 inactive, during costing system will give you message CK 424 'Material & in plant & has no BOM', even if you have BOM2 (another alternative) active. The choice is thus not 'either-or'.
The settings that I have indicated makes system choose the BOM as maintained in OS32 for the related application area, that is, in other words, OS32 provides you option to choose the BOM as per your requirement inside a validity period.
Hope this answers your query.
Best Regards,
Rajen