If we hadn't been dating all that long, I wouldn't be too concerned.
I've been with my BF for over 10 years. If he suddenly called me by another woman's name (on a regular basis, not just a one-off), there'd be trouble.
Once or twice, I'd attribute to stress or thoughts going faster than the tongue. Any more than that, and I'd be suspicious there was someone else in the picture.
Either way, I'd probably point it out to him and remind him of MINE!