What is the expected top marking on part number M24C32M-FCU?Is there a way to visually distinguish this part from M24C32-F once they're assembled on a board?

I am using ST1S03 in the inverting configuration shown in Design Note DN0011. Input 3.3 V +/- 7%. Output -3.3 V ~150 mA.I am getting efficiency only ~69-72%. Which, now that I look into it, is not much worse than the datasheet typical value of 70-75%...