In my presentation, I intend to discuss the records of the Kalisz consistory from the first half of the 16th century. Ecclesiastical court books are widely regarded as the most important source for understanding medieval Polish society, particularly its lower and middle classes, which are less accessible in other types of sources. At the same time, the vast corpus of surviving court records remains poorly studied from a source-critical perspective. Using the example of the records of the Kalisz foral officialate, I aim to explore the mechanisms and conditions that shaped the content of these institution's court books as we know them today. I will describe the institutional origins of the entries found in the records (which were not limited to those of the Kalisz official's court and its associated notarial office) and evaluate the completeness of these books in documenting judicial processes. The presentation will include statistical analyses conducted on over 6,500 entries.