Xbox Game Pass Ultimate 36 months prepaid on account question

Yep but there's a gap:

When you subscribe to Xbox Game Pass Ultimate, we’ll apply any prepaid time you have on Xbox Live Gold and/or Xbox Game Pass toward the Xbox Game Pass Ultimate plan, up to a maximum of 36 months. Prepaid time conversion rates are subject to change.

You can add the 24 months of Ultimate to your existing subscription as long as it won't go over 36 months. If it were to go over the 36 months, you would need to wait until you have 12 months or less remaining on your subscription before redeeming the 24
months of Ultimate.

https://www.xbox.com/en-US/xbox-all-access#faq

An Xbox All Access purchase includes 24 months of Xbox Game Pass Ultimate. So, what happens if I have an existing Xbox Game Pass and/or Xbox Live Gold membership when I purchase a console with Xbox All Access?

If you're already an Xbox Live Gold or Xbox Game Pass member, any days remaining in your membership(s) will be converted to Xbox Game Pass Ultimate at a conversion ratio when you redeem the 24-month Xbox Game Pass Ultimate membership and added to your Xbox
Game Pass Ultimate membership up to a maximum of 36 months. Xbox Game Pass Ultimate memberships are limited to 36 months.

If you’re already an Xbox Game Pass Ultimate member, wait until your existing membership has a prepaid balance that is less than 12 months before redeeming the 24-month Ultimate membership through Xbox All Access. You will be unable to redeem with more than
12 prepaid months of Xbox Game Pass Ultimate.

When you join Xbox Game Pass Ultimate, we will apply any prepaid time you have on Xbox Live Gold and/or Xbox Game Pass toward Xbox Game Pass Ultimate, up to a maximum of 36 months.

For example, if you have 3 months of Xbox Live Gold and 3 months of Xbox Game Pass already on your account when you purchase your first month of Xbox Game Pass Ultimate, you will have a total of 7 months of Xbox Game Pass Ultimate on your account before you
need to renew your membership.

https://www.microsoft.com/en-us/p/xbox-game-pass-ultimate/cfq7ttc0khs0?activetab=pivot:faqtab

Hey there JoshP3,

Thank you for reaching out to us on the forums, although we have had similar questions in regards to the new Xbox Game Pass Ultimate subscription we are always happy to help as this is new territory for all of us.

" 'What happens to my prepaid months of Xbox Live Gold and/or Xbox Game Pass when I sign up for Xbox Game Pass Ultimate'

When you subscribe to Xbox Game Pass Ultimate, we'll apply any prepaid time you have on Xbox Live Gold and/or Xbox Game Pass toward the Xbox Game Pass Ultimate plan, up to a maximum of 36 months. Prepaid time conversion rates are subject to change."

You can find more information for the new Xbox Game Pass Ultimate subscription by clicking on the link below.

Xbox Game Pass Ultimate FAQ

I hope this helps.

Did a bit more digging in the FAQs, no issues at all for existing Game Pass members (direct quote from FAQ):

If you're already an Xbox Live Gold or Xbox Game Pass member, any days remaining in your membership(s) will be converted to Xbox Game Pass Ultimate at a conversion ratio when you redeem the 24-month Xbox Game Pass Ultimate
membership and added to your Ultimate membership up to a maximum of 36 months. Xbox Game Pass Ultimate memberships are limited to 36 months.

If you’re already an Xbox Game Pass Ultimate member, wait until your existing membership has a prepaid balance that is less than 12 months before redeeming the 24-month Xbox Game Pass Ultimate membership through Xbox All
Access. You will be unable to redeem with more than 12 prepaid months of Xbox Game Pass Ultimate.

To check your prepaid balance, go to https://account.microsoft.com/services. Note, once converted to Xbox Game Pass Ultimate, Xbox Live
Gold and other Game Pass memberships cannot be unconverted. Learn more at www.xbox.com/gamepass.