Are not the terms Partition Type UUIDs and Partition UUIDs (PARTUUID) are the same thing? There can be a separate UUID for the filesystem (defined as UUID via blkid), that was the intended delineation here, if any as to not confuse anyone.

The Handbook states setting the PARTUUID is optional, so you can optionally set it. It may help 'future proof' your system if you want to keep the existing partition structure for other OS tools or distros. Using 't' to set partition types is to avoid the Generic Linux Data Partition PARTUUID of 0fc63daf-8483-4772-8e79-3d69d8477de4...

Hope this helps.