The inbreeding coefficient of a population, estimated from ecclesiastical Roman Catholic dispensations, results from the relative contribution of different degrees of relationships (uncle–niece, first cousin, etc.). The interpopulation comparisons of consanguinity patterns may be obscured by the fact that in 1918 the Roman Catholic Church norm regulating the closest marriageable kinship was modified, limiting the application for an ecclesiastical dispensation to relatives of third degree (second cousins) or closer. Depending on the length of the period before or after the change of regulation, coefficients and rates may differ. Deviation of frequencies for multiple marriages may also occur. The aim of the present paper is to determine how the chosen procedure based on ecclesiastical dispensations may affect results, regarding the inbreeding coefficient, the consanguinity rate, the structure of consanguinity and the close/remote kinship ratio. As a sample case, information from the Gredos mountain range (central Spain) has been used.