Think of your own writing. When you write to somebody, do you include their full title, responsibility, address, etc. each and every communication? Of course not. Neither would folks 2000 years ago. So in many letters, some of this information would be omitted, sure.
In short there’s no justification for elevating a job description to a title as Jesus said they were not to do.
It wasn’t just an oversight.
There were bishops, overseers, older men, but no Bishops or Deacons or Fathers, Reverends, Cardinals, Archbishops and the lot.