Well..here's the surprise...
When I started with YT I uploaded 100s of vids manually all from the same IP...no proxies.
Even the accounts were made with the same IP.
When a vid got banned I deleted 3-5 seconds from the vid and uploaded again from the same IP...and they stayed.
(until too many flags got them deleted again)
The same goes for my VA's later that didn't use more than a handful of my private proxies for uploading.
Nowadays I upload on autopilot...100s of vids a week...all from just 20 proxies that are rotated and maybe changed for 20 new ones every 2-3 months.
I read about problems with IP-blocking, vids deleted because of using the same IP, etc.
Maybe I am lucky, although I doubt it would hold over a period of more than 2 years...
Here's one observation: what I did notice is that premade YT accounts that probably used the same IP AND were made with a bot were banned in groups at the same time.
So maybe the IP detection on YT kicks in when you start creating accounts in bulk from the same IP. (if you can avoid the phone verification)
Who knows....it remains a guessing game as YT is not going to tell us...