I must disagree re allowable naked short selling by MMs. These are shares reported via reg sho and are legal as long as the MM did not have the required shares at the time of the trade and anticipates that the shares shorted will be available to cover within three days although there is no penalty for being late based on the market in a stock. . It gets tricky in the OTC as people are trying to track MM allowed naked shorts, retail shorting and offshore air shares ( which can not be tracked but certainly exist as many have been convicted of this firm of manipulation).