Not sure this is correct. For example: https://vanced.to/posts/youtube-premium-shows-ads-users-conc...

There's also this email from YouTube support: https://www.reddit.com/r/youtube/comments/1gnaetv/paying_to_...

It reads:

> While YouTube Premium provides an ad-free experience for most content, promotional ads can sometimes appear for specific partnerships or limited-time offers. These promotions are often targeted based on various factors, including your location, viewing history, and account settings.