$1 subscription promotion for game pass ultimate

That is the correct promotion. To get up to 36 months for 1€, you would need to have an active standard Gold or Game Pass subscription for up to 35 months. When you purchase the Ultimate subscription, the Gold/Game
Pass will be converted to Ultimate, giving you up to 36 months of Ultimate for 1€.

To clarify a little further, if he bought the $1 promotion it was for Game Pass Ultimate, not just Game Pass. Game Pass Ultimate includes Gold and Game Pass so if you already have a subscription for those when you purchase Ultimate, the remaining subscription
you have is cancelled and upgraded to Ultimate as well (meaning he would have had Game Pass Ultimate through December). By cancelling Game Pass Ultimate, it would have also cancelled his Gold.

The conversion is not tied to a promotion. Anytime you have a standard Gold/Game Pass subscription and then you purchase Ultimate, it will upgrade the subscription you already have into Ultimate at a ratio of 1:1. The other conversion rate that gets mentioned
applies when you are doing the opposite (adding a standard subscription to Ultimate).

No. The upgrade is not tied to any promotions or only for new members. Anything you have a standard Gold or Game Pass subscription and then you but Ultimate, it will upgrade what you have to Ultimate at a ratio of 1:1.

When you convert to Ultimate from a regular gold subscription or game pass subscription, it converts at a rate of 1:1. So for example, 12 months of gold would be 12 months of Ultimate.

When you have already converted to Ultimate and you add a standard gold or game pass subscription, that's when it converts at the other conversion rate.

@WPAK - The 1:1 conversion rate is included any type you upgrade. It's not promotion specific.