M.C.
I struggled so bad with plantar warts when I was young! For years, I tried every treatment, traditional (OTC treatments, doctor freezing them off, getting them cut out of my foot) and non-traditional (like the duct tape trick.) and they just kept coming back. At one point, I had 6 on one foot and 13 on the other. It was nasty. Even when I *thought* they were gone, they would come back. Ugh.
The thing I think finally got rid of them was garlic. I had resigned myself to having them, and stopped treating them at all. One year I went on a garlic dip binge, and went through about 3 cloves of garlic a week for about 4 weeks. (I really like the dip. Lol.) anyway, around he end of the last week I noticed that my warts were gone! And they still haven't returned 9 years later. :)
Sooo... Even if you can't see or feel them, there is still a chance they can return. Those buggers are stubborn! I would reccomend taking garlic capsules (or adding it heavily to your diet) for a few weeks, and see if that keeps them away.