[NSPS-643] Married couples in debt – Wife is embraced by a stranger 3 – Paid with his wife’s body

This series of four films began in 2011 when Nagae directed NSPS-122 Debt Couple I Had My Wife Hold On To Someone Else.

This version directed by B-Saku Sano 佐野B作 / Black Red Ginzo Sano B .

I’ve believed that the director credits are like that frequently where the cover is a Side B cover. But don’t know any story behind that. Does anyone else know why so many Nagae Style covers say Side B?