The oral tradition was certainly strong but there was no dearth as such of writing instruments. What makes their work not easy to access is their poetic symbolism, sun is one, moon is two and so on. These symbolisms were not even one to one, thus always leaving a window a doubt about what they really meant in their verses.
Since you mention Fibonacci, you may know what we call Fibonacci series was worked out around 250 BC by Pingala as an exercise in enumerating meter of verse
The oral tradition was certainly strong but there was no dearth as such of writing instruments. What makes their work not easy to access is their poetic symbolism, sun is one, moon is two and so on. These symbolisms were not even one to one, thus always leaving a window a doubt about what they really meant in their verses.
Since you mention Fibonacci, you may know what we call Fibonacci series was worked out around 250 BC by Pingala as an exercise in enumerating meter of verse
https://en.wikipedia.org/wiki/Pingala