Germline de novo or mosaicism?

"The current genomic sequencing standard is the need for at least 30-fold coverage, the authors suggested that at least 100-fold coverage is needed to identify true mosaic mutations present at an allelic frequency below 40 percent". This study believed that, an important fraction of de novo mutations presumed to be germline in fact occurred either post-zygotically in the offspring or were inherited as a consequence of low-level mosaicism in one of the parents. https://www.ncbi.nlm.nih.gov/pubmed/26054435