Ok, I hope you can get some good news for your next trial.
Now, something I just realized about you "expired" T5 lamp... From my limited experience in growing seedlings and observing them in the wild, I always found seedlings grew and thrived in very shaded condition. So is it possible your expired T5 lamp produce less light intensity compared to the non expired fluorescent lamp that could have actually produced light intensity more suitable to grow seedlings??? Hmmm....
