That's backwards. If the pulley loosens and lets the cam slide, the cam will be moving CCW compared to the pulley, which means the opening and closing of the valves will occur later; the cam is retarded, not advanced. You're probably thinking of what the cam timing tool indicates, which is fixed to the cam, as you rotate the cam CW, the pulley is moving CCW compared to the cam to advance it.
That said, I fail to see why retarding the intake cam will result in bent valves unless it was freely spinning between the hub and cam. :unsure: