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If this option is ticked, all packages created from that point will have the Locked Box option turned on by default. You can always override it by unticking it on a package by package basis.

Can I view all bids submitted by the Bidder after the Close Date has passed?

Yes, all Bids submitted by a Bidder during the Locked Box period will be accessible to the Package Owner once the Close Date has passed and the Bids are unlocked.