Our study establishes general statistical methods for estimating the accuracy of diachronic low-resolution satellite instruments for shoreline monitoring using the most common satellite datasets such as Landsat and Sentinel-2. The study coast is extended from Cape Araxos to Rio Port, in the Gulf of Patras in Northwestern Peloponnese, Greece. Landsat archival data from 1996, 2008, 2016, and 2018 (30 m spatial resolution) covering the entire study area were used consisting of images acquired by the respective instruments due the time such as the Thematic Mapper (TM), the Enhanced Thematic Mapper Plus (ETM+), and the Operational Land Imager (OLI). Moreover, for the years of 2016 and 2018, Sentinel-2 imagery with 10 m spatial resolution was used. High-resolution datasets of the respective years were used as reference for the calculations. “Generate near table” and “mean center,” two simple and fast statistical tools of the ArcMap v5 toolbox, were applied, and a comparison due to the relative results of shoreline change envelope (SCE) rates was performed. It is the first time that such tools are used to evaluate the accuracy of shorelines derived from low-resolution images. It was proved that the generate near table tool produces very similar results to the SCE tool of the Digital Shoreline Analysis System. There is a strong correlation between the two tools strongly dependent on the dataset being used (Landsat or Sentinel). The analysis of the Sentinel-2 datasets showed that the specific sensor can discriminate the waterline with better accuracy than all Landsat instruments and could be useful to relative studies especially when the procedure follows the subpixel level algorithms. Finally, the results showed that the upgrades of the Landsat instruments from TM to ETM and to OLI did not improve the accuracy of land-water delineation.