Upgrade Gold to Game Pass Ultimate?

I got Xbox Live Gold thinking that you can upgrade all the months you have of it to Game Pass Ultimate (the Xbox app says "Joining Xbox Game Pass Ultimate will upgrade your remaining Xbox Live Gold or Xbox Game Pass membership(s)
into Xbox Game Pass Ultimate for the same amount of time, up to 36 months total"). When I go to get Game Pass, it says I will only get 2 months free.

:)