The coefficients of coancestry and average relatedness are two useful tools to define in practice appropriate mating decisions aimed to control inbreeding rates. However, their utility is conditioned by the amount of genealogical information available, since, if genomic information is not employed, the accuracy of both coefficients depends on the genealogy completeness. In incomplete pedigrees with animals differentially affected by missing information, the accuracy will vary among them and this will affect mating decisions. The aim of this work is to compute some reliability measures of estimation of coancestry and average relatedness coefficients. Two measures are proposed based on the proportion of known ancestors of an animal in five generations, and the use of genetic group concept to integrate known genealogical information not included in pedigree. Results show how these measures can help to improve decisions on parents' selection and mating.