It certainly is an interesting question, bearing in mind the difficulty experienced in solving the 50-year-old 340 cipher and the still unsolved 18 characters at the foot of the 408 cipher. The Zodiac Killer stated in the 408 cipher, preceding the final 18 characters, that "I will not give you my name because you will try to slow down or stop my collecting of slaves for my afterlife". If the unsolved section of the 408 cipher didn't contain his name or identity, is it possible these 18 characters were supposed to bleed into the message on the 340 cipher. This has to a realistic proposition when we consider the 340 cipher begins with the final three letters of the word cipher. Was this just another coincidence - or did each cryptogram share half of the word cipher, as well as sharing a message? It is a compelling argument that the Zodiac Killer may have intended to leave only 12 unsolved characters at the foot of the first cipher (possibly decoding to "I am the Zodiac"), but the accidental omission of the word people from the message may have resulted in an unwanted extra 6 characters, thereby forcing a change of plan. Could the 18 characters now form part of a 21 character bridge (or more) between cipher one and two? The 408 cipher ending with cip and joining the her of the yet to be released 340 cipher. If the remainder of the 408 cipher and beginning of the 340 cipher was somehow conveying the idea of "sorry no cipher", in similar fashion to the October 27th 1970 'Halloween' card, then the message on the November 8th 1969 greeting card stating "I thought you would need a good laugh before you hear the bad news", may be pertinent to the cipher that accompanied it.
By extension, from the Halloween card to the 340 cipher, was the Zodiac Killer telling us that the second cryptogram was "sorry no cipher"? And by extension, was the Zodiac Killer telling us exactly the same thing from the 408 cipher to the 340 cipher, hence the tantalizing her at the beginning of the cryptogram. It could be argued that the placement of her at the beginning and the near-Zodiac towards the end, is a little too convenient. A message of "sorry no cipher" through three sets of communications may be a bit difficult to shake off as coincidental.
If the Zodiac Killer created a rambling message akin to the 408 cipher and randomly allotted his cipher key, then he was extremely unfortunate to have crafted the possibility of the configuration on the right, involving the words paradice and slaves, by in each quadrant, with her at the beginning and Zodaik near the end. This is not what you want to achieve when you are trying to convince the world it's a genuine cipher, because people like me come along. The prospect of finding the same mini-message shared between the 408 and 340 cipher, that was found on the envelope inner of the Halloween card would certainly be "bad news" for some.
I would like to thank David Oranchak for his contribution regarding the Cryptologic History Symposium, and would encourage everybody who is interested in ciphers to click the highlighted link. Below is just one rudimentary example I have drummed together, using a screenshot of the Youtube video, keeping 7 of the 21 characters in their original format.