surface polishing granite tiles

hello- i am a professional stone/tile installer, and often install 12x12 granite , and polish edges etc etc...however, occasionally, i need to do some surface polishing, for a scratch, or to polish out an epoxy fill to a chip or something, and some granite tiles appear to have been 'coated' with some type of 'resin' or finish of some type, in the manufacturing process, in order to give the piece a better shine and to hide the natural pits (like some uba tuba on this job), in fact if you flip over a piece you can see the resin drips from the surface.  so- my problem is, when i surface polish this type of stone, i can not get it as shinny as the factory resin areas...even if i go to 10000, and even then put on some enhancer. is there anything i can do, short of not working with coated materials?  it also seems the coated granite is a lower grade, more pits, less stable, more prone to chipping during edge bullnose/polishing, more cracks, etc.  also- can you can you confirm this coating process exists, and is it a low grade granite, and should it be avoided, and how does it effect sealing, should a pen.sealer be needed?  also it seems a 12x12 piece of granite may have been top coated in the manufacturing process where its slab counterpart was not.   thanks for your time. jason