Update old leadership position

We have a former youth who turned 18 in April. When we added his ASM position in TT, we forgot to put an end date to his last position (instructor). We don’t seem to be able to edit any position other than the current one of ASM. Is this a bug? A design flaw? Or are we doing something wrong?
Also, shouldn’t his leadership show up chronologically? It appears to be alphabetical.