As of Wednesday morning, it's been somewhat fixed. Brands can now fill in their Timelines back to the year 1000.
The problem only plagued the pages of brands that predate the year 1800 -- the U.S. Army and Navy, Princeton University, and the Church of Ireland, to name a handful of examples. We didn't notice the problem until Timeline rolled out for brands, because no individual person using Facebook today was born before 1800 (unless we've got some vampires, time travelers or highlanders among us).
Eagled-eyed Mashable readers noted the change this morning:
Well look at that: @mashable does a story, and @facebook changes its timeline start year to 1000. #webpower— Stretford End UF (@UFStretfordEnd) March 7, 2012
Another reader set up a simple test page, clearly showing a "started on" date of 1000 A.D.
Previously, older brands were using 1800 as their "start date," adding caveats explaining their actual, much older origins. Here's an example from the U.S. Army:
“At this time, this page only allows us to go back to 1800,” reads the U.S. Army’s earliest milestone marker. “However, we were ‘founded’ in 1775.”