I've had three different pairs -- two sounded about the same, one did not. The one that did not was excessively bright and fairly bass-light. However, never did any of these T1s change their sound signature over time -- to use the terminology that's being tossed around here, the "normal" ones continued to sound "normal", and the "defective" one continued to sound "defective". And never once did any of them sound as dark as or darker than an HD650.
Do you remember the approximate S/Ns of any of them?