Roller cam/lifter problem

My block had 3 lifter bores that were counterbored at the factory when the block was cast. All the others were not. Not exactly sure why they did it, but I've seen other blocks with this same issue and some with no counterboring at all. The ones on my block were all drilled at different depths too so it must have something to do with how the block came out of the molds as to whether or not this added step needed to be done. I was on the edge of having one of my lifters oil band exposed but just the one. Others here might have a better understanding as to why the factory did this. I believe Hughes Engines did a tech article on this?