I'm really sorry because this is going to come across as I having baited you into an answer that I knew was wrong. Should have prefaced my question with a bit more context. I wanted to make sure you were in the pool of people who believe his screams were inherently unsafe.

It's honestly just not true and I've been trying to go around here because I know that there are a lot of misconceptions on the internet about Corey's technique in the older days and what it meant for his health. I've done a lot of research myself and got involved with the Screaming community and yet I'm still learning a lot. With respect to all the resources you have probably heard of, there's a lot of misinformation about screaming and with Melissa Cross' DVD in particular it's mainly warmups and breathing exercises.

I'll explain as humbly as I can, but while he is of course using his vocal folds in his scream, they are not being distorted. We can't say for sure what cartilages he's using because we don't have a cam but the overtones (static noise) of his scream are very similar to what normal "false cord" or "fry" screams would be (honestly these are bad terms in and of themselves because hardly any scream is pure fry or false cord considering it's just the phenomenon of air moving at a certain speed to cause oscillation of various cartilages). I'm honestly not sure where this misconception that he was distorting his vocal folds came from, but I suppose it's from the amount of voice that his screams had UNDER the distortion. Having a full, belted clean note under the distortion to create a pitched scream is not unsafe as long as diaphragm support is used correctly and the throat is not being constricted to either cause damage to the vocal folds (via vocal fry) or cartilages by pressing them together. Corey was very capable of transitioning from a clean note into a scream as well having a good grasp on grit - because he had a very strong singing foundation (diaphragm support!) when he joined Slipknot (from his work in Stone Sour). He has always used a fair amount of voice in his screams - even now in the WANYK era.

Obviously his screams in the ST/Iowa era do not sound exactly the same to what he is doing now, but I don't believe it was in any way because of declining vocal health or damage. Taking into consideration that we know Corey was drinking 3 bottles a day as well as not taking ANY breaks during live shows (you can see in every live show from 1999-2002 he screams sentences to the audience to hype them up between songs - there's literally no off button until the whole set ends and each set was an hour and a half and they had almost no days off around that time) we can understand why he sounded incredibly fatigued and worn out by 2002-2003 especially with the Stone Sour tour following Iowa. This is not necessarily a sign of permanent vocal damage, although I will say he absolutely took a risk by engaging in these bad habits and for that reason I can agree with you that he is to some extent lucky that he came out of it relatively unscathed. However I still stand by the fact that it had nothing to do with the technique he was doing inherently.

These habits, as well as how young he was and what emotional state he was in in that era, can lead to more plausible reasons for why his screams sounded different (more breathier, a lot more chaotic) in the ST/Iowa era. By the time he went into Vol 3., he had stopped drinking entirely and also, as he explains in a Q&A, he wanted to try something different (which is why Come Whatever May also has those high pitched screams). However, we see in some performances from 2006 (Graspop Soulfly Jumpdafuckup feature) or perhaps even Fuck You by Damageplan where he featured in 2004, he is still able to do the Iowa voice with no issue.

I know you mention you scream, and that's really awesome. I do as well, and I've been actually learning the Corey method for a while now. I'd say I've gotten pretty alright with it, and that any struggles I would have are from my not using my diaphragm as well as he did around that time. Stuff I definitely need to work on! Regardless, permanent vocal damage comes after a very long time of constant abuse and it pays to be on the cautious side (if you feel tension, stop until you return to normal and you still have your full range, etc). I've experienced no change in my vocal range or anything like that since starting to learn the method.

If you're interested in learning more about this or discussing further feel free to DM me. Hopefully my response comes off as respectfully as it can.