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Genes important for research and breeding new plant varieties are crucial for the survival and development of human civilization. Seeds of cereal germplasm are maintained in gene banks (GBs) and grain viability of GB accessions must be regularly restored by seed multiplication. During related operations human errors result in contaminated or mislabelled accessions and thus in genotype non-authenticity, and such mistakes accumulate. The detection of non-authentic genotypes in GBs has been a major topic of our research. In this article 289 accessions of 93 winter barley varieties were studied, each obtained from several of the total of nine GBs (on average 3.1). Five single seed progenies (SSPs) were usually harvested from an accession and their genes of specific powdery mildew resistance were postulated. In 1,412 analysed lines 22 known resistance genes and 60 of their combinations were identified. Variety accessions from different GBs were compared; 40 (13.8%) were mislabelled and 102 (35.3%) heterogeneous, both containing a minimum of 276 SSPs (19.7%) carrying non-authentic genotypes. In 93 varieties 273 genotypes were found; 68 (73.1%) varieties were heterogeneous, containing from two to eight, (on average 3.6) genotypes. Misrepresented varieties in GBs are a great problem for research projects, especially those aimed at finding new (e.g. molecular) varietal characteristics, and in breeding programmes as the required gene combination of bred varieties cannot be achieved. A suggested way to allot responsibility for use of authentic genotypes is proposed.