I came to the conclusion that it is quite possible that the phrasing "4-teen" comes to indicate that by October 27th, 1970 the last victims to be added into the zodiac’s list were 4 teenagers, now we have to isolate them from all the murder victims in the time frame between that day to the April 20th, 1970 communication ("my name is" letter) when the "score" was 10. That’s why the 4 eyes in the left side of the letter were drawn so close to the text and outside of the "plank" on the far-left (those eyes represent the previous victims, if you’d look closely you’d see that the 4th eye which allegedly represent Cecilia Shepard is within the dark hole as to represent his dark costume from that murder).

Not that he break his pattern of murdering UNARMED INNOCENT TEENAGERS, he was still the same low-life dirtbag who preyed upon those whose lives were still ahead of them and 99.9999% succeeded more than him in it.