Ok let's say your character's name is Jon and you are on ServerA.
You create a mule named Jon on Server B then switch to it and rename your original character Jack. Now in 3 months, if you go back to Server A and create a Jack mule, can you choose Jon as your new name? Are names that have been chosen before but deleted or world shifted still stored on the server as "In Use". Assuming no one chooses the name Jon in the 3 months you're gone, couldn't you in theory change your name back to Jon when worldshifting back to Server A?
XI Wiki

