The seed of 2b2t when it started was -4172144997902289642, and was on August 8 2011 changed to -1373982429803982829 following the player data corruption. The seed was eventually changed back to -4172144997902289642, but the date this happened is currently unknown. It must have happened some time in 1.0 or 1.1, due to 1.0 terrain generated with the second seed existing, and 1.1 terrain with the first seed existing. This puts the date it changed to sometime between November 18th 2011 and March 1st 2012.

Back then, the world seed was displayed in the F3 screen making it very easy to tell when a seed was used, provided you have a screenshot showing F3. I am therefore asking if anyone here used to play in 2011-2012 that still have screenshots using F3 from this time period. I doubt any are, but it's worth a shot.