No official leadership positions

I was talking to a mentor and mentioned how I didn’t have any official leadership positions. I have trained other MA’s at my job since I’ve been there for over 2 years, but I wasn’t planning on listing that as leadership because I figured it was just part of the job as an MA. My mentor said that I should list it anyway.

Would that be appropriate to list training other MAs as leadership despite it not being an official position? And would it look bad to not have any listed leadership positions overall?