I just asked pretty much the same question and here is the answer: This is an example of how it stands in my case.
Hello,
Yes, if you choose the upgrade located at Upgrade Advisor – Pantheon – Rise Of The Fallen (pantheonmmo.com)
It will only charge you the difference between pledge levels.
Thanks for contacting Pantheon Support
Thunderleg said:
I just asked pretty much the same question and here is the answer:
Hello,
Yes, if you choose the upgrade located at Upgrade Advisor – Pantheon – Rise Of The Fallen (pantheonmmo.com)
It will only charge you the difference between pledge levels.
Thanks for contacting Pantheon Support
Just to help avoid any confusion, I would point out that the link in the quote above is not the correct one for Toastsniffer. It is the correct one for someone who has an Advisor's Pledge. The rest of the info is correct and does apply to anyone wishing to upgrade, though.
The generic link for anyone to upgrade their own pledge is here: https://www.pantheonmmo.com/pledge/upgrade/
It asks for what level a pledger is already at, then gives the info for upgrading that pledge.