I've watched the Del Mar Thoroughbred database develop over the past several years and have seen that phenomenon in action. It did make a believer out of me. I hate to be the bearer of bad news, but there are literally thousands and thousands of errors in both. Trust me, I've worked with pedigrees for 30 years and never quit discovering mistakes. For the most part, it's very understandable.
Part comes from trying to put old handwritten records into type.
Others are probably typographical errors made when AQHA first computerized their pedigree records. I doubt the data input people were familiar with bloodlines, so even a major blunder could be entered without a clue. That would be like having a chocoholic clerking the candy store. Use the database with caution and common sense. Kudos to Miles for developing such a wonderful set of tools for breeders.