Editting a calendar chaired by another user

I have a user that used to have a Blackberry. He now has an iPhone6+ and he's not able to edit calendar entries that was created by another person. He was able to before on his BB. If he creates the entry, he's able to edit the entry but if it's created by another he can't edit. All he wants to do is just add comments for his own reference. Sometimes he copies/pastes these Notes and resend it to the entire invite list. He can't do this right now. Any chance this is possible on the next version so iCalendar. He currently has the latest OS 8.2.

Thank you!