I just got 2 free Charm Factor lipsticks through B2M by turning in 12 empties to the MAC counter at Nordstrom. My empty e/s pots didn't have the metal pans in them either. No MA/SA has ever even checked what my empties look like, honestly (not at Nordstrom, Dillard's, Foley's, nor the freestanding MAC store). I have only had a problem one time getting a LE lipstick through B2M, but it was a special promotion for The Girl Next Door movie. I know others on MUA, though, who got TGND lipstick free through B2M, so it really does depend on who you deal with and what store/counter it is.
I try to stick to the SAs/MAs that know my face, know I'm a "MAC addict," and won't give me a hard time about getting a free lipstick after I've literally spent thousands upon thousands of dollars on MAC.