That is incorrect information that is based on old data. While fluidized bed drying is indeed hard on yeast cells (which is why we do not enjoy as much variety with dry yeast as we do with liquid yeast), the reason why dry yeast used to be a no-go with repitching had to do with the level of contamination commonly found in dry yeast cultures. Basically, dry cultures used to pick up microflora other than the target strain during the propagation and drying processes. The problem with repitching any yeast culture with low levels of contamination is that every propagation event is a chance for non-target strain microflora to grow as well. That being said, dry yeast propagators figured out how to produce dry cultures with a high level of purity in the mid-nineties. Dry yeast is routinely serially repitched today.