Maybe check your thread tools in the FAQ up top left side of page.
I just checked mine and the threads all go back to 2006 which is the beginning. If you're viewing the forum offline though, it won't show older threads, it only shows a few.

There's an area in User CP up top left, where you can make changes to your own settings .

So go to
User Control Panel
Settings and Options
Edit Options.

Scroll down to Thread Display Options.
e.g."Use this option to set the number of posts to show in a thread before splitting the display into multiple pages."

You can set to show 5 posts per page all the way up to 40 posts per page. At 40 posts per page I ended up seeing 224 pages of threads all the way back to August 2006.

There's also
Thread Display Mode.
and
Default Thread Age Cut Off.

Mine is set to show all threads. The other settings vary.

Maybe check your Default thread age cut off first.