This question is only the latest of a re-curring kind of question: too many notes in a bar due to multiple voices in one system. It is quite difficult to find one of the numerous duplicates due to lack of a convincing tag.
None of the poly* tags seems appropriate, neither multi* (multitrack would somehow fit, but is unlikely to be considered by somebody asking) and the *voice* tags all imply singing.
This leaves notation and time-signature (or even an instrument-specific like piano), which have already a quite broad scope limiting their usefulness for searches.