Barry Fell, et al, were always looking for alphabetic systems imagining that it'd have to be Mediterranean people who managed to get to the Americas by boat.
On the other hand, there was an ideographic/pictographic system in North America that was exceedingly widespread and almost totally ignored. It's called North American Indian Sign Language. Many of the ideographs you form (using your body ~ arms ~ face ~ legs ~ hands) are remarkably similar to old Shan Dynasty ideographs.
I think that gives a date to that system and its underlying linguistic components.
I took my Sign Language book with me to an exhibit at the Smithsonian some time back of a number of Shan "documents". Before the internet it was difficult to get access to these things but I guessed i'd want to have my book with me to see if, perhaps, there were characters in common.
Yup, there were characters in common. I stood there with a group of Chinese who'd come to the museum to see these ancient heritage pieces and read to them what was on the pieces on display ~ using my book. They all wanted to get that book!
I have two theories about this ~ that at some time in the past 7 millenia Shan users/writers came to America or that both fundamental systems are based on "natural structures and processes" and those are the same wherever you go.
Problem with that latter theory is you'd need to explain why that never occurred to anyone else.
BTW, when the Shan civilization/dynasty fell and people fled, they may have made it to America. More recently they've found all sorts of Austronesians, Polynesians, and Europeans who made it to America THOUSANDS of years ago, or as recently as the 1100s, 1200s, 1300s, etc.
They simply didn't go home, nor did they leave many records. After all, what were they going to say? "Hey, mom, I'm lost, send daddy" perhaps.
Except for the cocaine salesmen who seem to have traveled from the Americas to visit ancient Egypt, there's very little to even indicate Mediterranean civilization was interested in going to places with inferior weather.
“They did not leave many records.” If that is what you think, then you really need to see Gloria Farley’s book.