This thread has nothing to do with my geckos or whether or not my original geckos were quarantined properly. It was simply a thought in my mind that made me curious. Thanks for the input.
My previous statement did not say anything about your geckos, as you can see it has not been edited. It is true of stores placing new shipments in with existing stock, as well as a pet owner bringing home a new animal. That is how diseases spread to otherwise healthy animals. At reptile shows this is why you see bottles of hand disinfectant at every vendor's table.
Furthermore, if it is a one animal home, disease can be introduced by feeders such as crickets. Some diseases can also be present but not show themselves until the animal becomes vulnerable due to some environmental changes. Bacteria can grow on some housing items that could cause an animal to get sick. Many things are microscopic, so we don't see just what's going on until there's a symptom detected.