Considering how much verbiage is dedicated to safety warning on my 2 ton stands, I'm sure there would be a clear warning if they were't meant to be used all the way down--and there is no such warning.
BTW: If you're using jack stands where you're subject to OSHA inspections, be aware that the stands MUST have the stickers with load rating present and in readable condition. Our last OSHA consult resulted in me having to toss two massive, heavily over-built, 30-year-old US-made stands into the scrap dumpster while the inspector watched (they came back out and went home with me), while he was fine with the Chinesium ones with readable labels.