The traditional definitions by linguist tend to exclude anything that can't represent "all oral communication" as proto- or partial writing systems, which are o

The traditional definitions by linguist tend to exclude anything that can't represent "all oral communication" as proto- or partial writing systems, which are often pejoratively labeled mnemonic systems. Systems that can represent the full range of spoken expression are labeled "true" or "full" writing. This had the convenient side effect of neatly classifying all the American writing systems as protowriting in the early 20th century, as well as some more controversial examples like Chinese. Some of those have since been walked back (e.g. Mayan), but most remain in that limbo. We have a somewhat better understanding today that there was a huge variety of visual communication systems across the Americas prior to European contact, but properly redefining the term "writing" to include them is a slow, ongoing process.