I'm not sure if it's a legal requirement, but YouTube has the rule that once a channel gets 3 DMCA takedowns (without counter notification) within 90 days, it will suspend the channel. Such a warning is usually referred to as a copyright strike (not to be confused with a copyright claim or a community guidelines strike).
One difference between the Google index and YouTube is that links in the Google index can be service providers like YouTube, while the owner of a YouTube channel is always the one responsible for the content.
Something notable that happened here is that instead of bundling the 5 videos in 1 DMCA takedown resulting in 1 strike, the party sent 5 separate DMCA takedowns causing 5 strikes.
One difference between the Google index and YouTube is that links in the Google index can be service providers like YouTube, while the owner of a YouTube channel is always the one responsible for the content.
Something notable that happened here is that instead of bundling the 5 videos in 1 DMCA takedown resulting in 1 strike, the party sent 5 separate DMCA takedowns causing 5 strikes.