I looked for information on this (both by reading thread titles and through Search) but didn't come up with any: I'm wondering if I can change the setting on a sub-board AWAY from the "No unread posts" designation that seems to apply automatically to all threads of a certain age, regardless of whether I've ever looked at them or not.

I noticed while reading around on the forum that even in sub-boards (for particular movies, say) that I hadn't visited before, all threads older than a certain time period were designated as "No unread posts". This function makes it harder to keep track of my reading on the site (as I don't know, when coming back to the sub-board after a period of time, which older threads I've looked at and which I've never clicked on.)

I looked all through my Control Panel settings (beginning with the Board Preferences) and couldn't see a place to make this change.
Then I tried clicking the "Mark topics read" button at the bottom of THIS sub-board--hoping that the button would then change, offering the option to "mark all topics as UNread"....but, no.

Possibly the site software doesn't offer this option. But I thought I'd ask, before abandoning hope!