Did a bit more research on academic sites. It comes down to the PV module components, “The low light behaviour of a solar panel is mainly dependent on the shunt resistance and series resistance of the cells”. All of which seems to relate to quality & cost of circuits, resistors, individual cell material used in a PV module and consistency/quality of material used by manufacturer. Apparently standardised testing is conducted in laboratories with software analysis of PV Module performance.
Thus it seems, cheap PV modules are unlikely to be low light power producers, mid range ones are anyones guess and expensive ones might produce 10% more power over their life. Based in techniques and materials used today to manufacture PV modules.