Carl, the burl will usually have some voids in it, but good quality maple burl like I bought from TKS all voids were filled with resin, but there were hardly any voids at all. It will begin with the piece of wood you start with and some will just have voids. Where did you get your last pieces from and what kind of wood burl? I only ever bought from TKS and cannot speak to others.
I usually just use exotic hardwoods that do not need to be stabilized like cocobolo, ironwood, african blackwood and a, favorite tulipwood. Some rosewoods like purple heart, padauk or cocobolo are oily and need to be wiped off with some solvent before gluing and use pins or small corby or loveless screws. I go to a Woodcraft Store over in Knoxville to buy my wood as I like to pick it out myself. Even some exotics need stabilizing like some types of ebony are very brittle.
Here is K&G's website
http://www.kandgstabilizing.com/gallery.html