I've seen this question come up several times. My take on this issue is that people often forget the patients in this shuffle. Imagine you're on Medicare and you are coming in for what you think is a "free preventive visit". During the course of the visit, your provider is addressing your other concerns, but leaves it at that. A few weeks later you now have a $300 bill in the mail, for what you thought was going to be free.
Since our patients are essentially our customers, how can you improve this customer service? From the provider side, if you already know this might turn into at least partial E/M, inform the patient and let them make the choice whether to reschedule or expect a bill on the E/M portion (which should probably be a low level E/M anyway if billed with an AWV). If I went to the doctor for what I thought was a preventive visit, and I was on Medicare but then suddenly ended up with a $300, I would be upset. I had an AWV provider who would at times bill a 99215 instead of an AWV because of insurance issues or that the AWV was billed too soon. Needless to say, her patients were very upset with her.
Coding-wise if documentation supports both codes, then you can/should definitely bill as appropriate. However, have the provider give the patient a heads up first to avoid any frustrations down the road. It's just good customer service and a win-win.