Based on @blackkatmagic
Jedi can end up anywhere and may be out of contact for a long time. So there are times when the temple jedi don't know if they are alive or dead. Things happen so if a Jedi isn't in contact or seen for a while they say they joined the force. Unofficially of course. Only when body or proof is when they are declared dead.
All this so I can make a joke about how sometimes Jedi can still hear the voices of those that joined the force only for that person to pop up and tell them to stop telling everyone they are dead.