Many Reborners think it is essential to remove the molded hair lines from the head of the doll. This is one area where I think the ladies have gone to an unnecessary extreme. Most of the Berenguer dolls have little or no molded hair marks so they're not much of a problem. If you sand the doll, there are quite a few risks involved. You can punch a hole through the vinyl head. Or, the vinyl becomes thin and weak so it might break later on during the hair rooting process. You might scuff the vinyl on the doll's forehead and then you will have problems coloring the vinyl in those places.
I have seen many vintage dolls with molded hair underneath the rooted hair: this is nothing new. I know that the Reborners go to extremes in their quest for "realism" but I do think we should remember that this is just a doll. It may not be a good idea to sand down the vinyl. It may even be toxic, because of the fumes and vinyl dust that could be inhaled.
If some ladies choose not to sand the heads, I don't think it should be held against them. The Reborn Art has a tendency toward cult fanaticism. This is partly due to a high level of competition on the eBay market. I don't think we need to go to all extremes in order to be a good doll artist.