Are the XYZ states unconventional states or conventional states with unconventional properties?

Understand

We discuss three possible scenarios for the interpretation of mesons containing a heavy quark and its antiquark near and above the first threshold for a decay into a pair of heavy mesons in a relative $S$--wave.

• View I assumes that these thresholds force the quark potential to flatten which implies that while in these energy ranges molecular states may be formed there should not be any quark--anti-quark states above these thresholds.
• View II assumes that the main part of the interaction between two mesons is due to the poles which originate from the $Q\bar Q$ interaction.
• The properties of the $Q\bar Q$ mesons are strongly influenced by opening thresholds but the number of states is given by the quark model.