Carpet cleaning question

I recently purchased a Hoover "SteamVac" to clean my carpets. It did a superb job, making 17 year old carpet look like it is only about 1 year old, except for a few really bad stains.
There's a mystery, though. After cleaning the carpet, there were several bad stains that appeared. In other words, the carpet was so dirty previously that the stains just blended in with the dirt, so they weren't visible until the carpet was cleaned. I recleaned and recleaned those stains, but they just would not go away. In fact, they seemed to become even more obvious. In desparation, I sprayed some "Goof Off 2" on to the persistent spots. I thought that maybe the "Goof Off 2" would loosen the stains and I would be able to blot them up, like the directions say. Instead, the stains just disappeared in about a minute without a trace. There was nothing to even blot up. The carpet has dried and the stains are still gone.
Can anyone tell me why the stains disappeared? This was totally unexpected, although I'm pleased, of course.
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Some of the new oxygenated spot removers (Woolite makes one) are good at getting out old stains. Bissell has a new 2 part aerosol that works well too. Your Goof off probably bleached the stain out. If it isn't recommended for carpets you are probably lucky you didn't ruin the backing.

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