Hi -- Thank you for pointing this out. It is a typo in the documentation and has been corrected.
Yes, your current co-termination date will be applied to all the devices currently in your organization. Then, after you convert, when you add another license (e.g. a 7-year license) to a new device, it will have a separate date compared to the devices/licenses that were converted.
"Current customers will not see a change in their expiration date when they convert to per-device licensing. When they purchase a new license/device and claim it into their organization, is when they will see a different expiration date. For example, if the customer's co-termination date is 1/1/2025 and they convert, their expiration date in per-device will be 1/1/2025 for all their devices/products. If they purchase 1 new AP with a 7-year license on 1/1/2020, the expiration date of that device will be 1/1/2027. The other devices will maintain the 1/1/2025 expiration date."