@userZArN3oCbTj @Wolflaguerra @Kletimostaph you have to make a new Google account in order to redeem the 4 month promotion if you have had any sort of free trail in the past, no matter how long ago it was. After I made my new Google account, I was able to get my 4 months of YouTube Premium. Hope this helps!
@Wolflaguerra also be advised it may not show up immediately. When I first made my new account it was only offering my 1 month. A couple hours later the 4 month promo appeared. This might not be the same for everyone though.
Signed up for the premium and did not get 4 months. Got the standard youtube trial and like most of the people on here that have checked with multiple accounts, ranged from 1-2 months free. I have never signed up for premium ever (it's just another streaming service I don't need, but I figured, heck, why not for 4 months).