I had my wrap in February 2009, and can only speak for myself. At times I get an irritated feeling at the wrap level that sure feels like heartburn. I notice it when I've eaten badly, or too much, and irritated my wrap. If I drink coffee it will sometimes feel that way--sometimes not. I still feel the need for Maalox at these times. Sometimes it occurs at night...or my wrap wakes me up with some pain sensation.
My asthma was made uncontrollable by my pre-nissen GERD, and the heartburn that I'm experiencing (very occasionally) is not sending acid up the way it used to. My asthma is unaffected. Even when I burp, I'm not getting acid...sometimes if I drink lots of water, there might be a little pool at the bottom of my esophagus, which pops up a little--but no acid.
There is always a chance that some acid is making its way through the wrap, but it is also possible that the esophagus/wrap is reading the irritation as heartburn, when it's not true reflux.
I think that it'll be a good year before our wraps are as healed as they're going to be. Until then, anything can occur...there is sure to be some swelling at times, even at this late date. The GI tract is just settling into its revised form.
No matter what the cause of the "heartburn" sensation, there's no doubt that I'm in a lot better shape than I was pre-nissen, when my asthma was so bad that I needed high doses of steroids and a nebulizer just to be able to breathe. I wish I'd done the surgery long ago, so I could have avoided the exposure to the high steroid doses. It has left me with very thin skin (the skin of a 90 year old) that bruises and tears easily. I was afraid to do the surgery because of all the negative and hysterical posts that were all over the internet. I was glad to find this site where people with experience had positive and supportive attitudes.
Good luck. I don't think you need to worry.