Download Group List question

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Can you explain how the download group list works? What is the criteria for Group Date Added? When I run it and sort by date added, I see a lot of groups showing 00:00:00, but a lot of them are groups that I've seen before in the list. Like ALT.BINARIES.WELOVELORI and ALT.BINARIES.USENET-SPACE-COWBOYS. I use these examples because they have really unique names and are hard to miss in the groups list. They always show as just added.

thanks