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This means your cache has reverted to whatever the master cache for that page is. August 3 is a reasonable date for the current master cache for a page.
That, at least, is my experience but I haven't bothered to observe this behaviour for a while.
Unless these pages are updated and spidered, they'll revert back in a few days. They'll jump forward again as they are fully integrated into the index.
On most of our sites a lot of the content is refreshed every 48 hours.
I use a server side date to check this...