Thanks for the new messages!
In the 340, there are one period 6, two period 13, four period 26 and one period 39 repeats spaced at 78 positions. So I decided to look at all of them at once and without all of the other symbols.
Period 6: Grey shaded orange bordered 51 and grey shaded blue bordered 53.
Period 13: Orange shaded 19 and grey shaded orange bordered 51.
Period 13: Grey shaded orange bordered 51 and orange shaded 19.
Note that grey shaded orange bordered 51 is common to the period 6 repeat and both period 13 repeats, and the period 13 repeats are actually a period 13 trigram repeat spaced at 78 positions. My symbol 19 is the + by the way.
Period 26: Purple shaded 17 and purple shaded 15.
Period 26: Yellow shaded 5 and yellow shaded 36.
Period 26: Orange shaded 19 and orange shaded 19, which are also common to the period 13 repeats / trigram.
Period 26: Grey shaded blue bordered 53 and blue shaded 11.
Note that the grey shaded blue bordered 53 is common to the period 6 repeat.
Period 39: Green shaded 14 and green shaded 48.
coincidence.counting.29.png
You can see some interesting patterns with these symbols, including one period 19 bigram repeat and one period 19 trigram spaced at 78, which are the only period 19 spaced at 78.
I still don't know if the coincidence count spike is a rabbit hole or if Bart detected a transposition or other cipher. Bart, maybe you were detecting these symbols when you were talking about 6, 13, 26 and 39?