there is a youtube video of the td-3, an original tb-303, a xoxbox, and another clone side by side by side by side if you're interested.
He did mention in the video there is supposedly a ~10% variance between original copies. But, to my ears, the original tb-303 was a bit mellower on the lower end of the frequency range when sweeping the filter. As if the envelope was tracking lower maybe. Might be the variance he was mentioning..