It depends on the source of your "permission". If for example the permission is via a public license which say "must attribute" without being more specific, then the question is whether your efforts to comply with that requirement are "reasonable". Observation of typical attribution statements will tell you what is reasonable (because it is assumed that most people are reasonable). If it is customary that attribution statements include information such as "URL1 of ours comes from SOURCE1; URL2 of ours comes from SOURCE2...", then that would inform you of one reasonable outcome. Alternatively, if it is customary that items simply be acknowledged somewhere, e.g. "We thank SOURCE1, SOURCE2... for permission to reproduce their stuff", then it is reasonable to limit the attribution to that. Mainly: whatever the license says; secondarily, whatever is "reasonable" in case a specific detail is not stated in the license.