I'd like to know as well...（＞人＜；）Credits are important! Some of them might even be illegal redistributions, who knows? ヽ（≧□≦）ノI'm interested by some of them!!! I would like to download from the original sources!!!
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Theres no way to know, its all mixed from over a hundred sources. Its been over ten years since I collected them and I don't even remember the sites, if they're even active anymore, nor if the people are even alive.
I've updated the description to make it clear that you should not use these for commercial solodev projects unless you're feeling brave.
For community modding projects, art-style inspiration for your own art, its all fine.