The Catalog Red Sísmica del Noroeste de México (RESNOM), operated  by CICESE is investigated. Probable artificial effects are detected. Current values for minimum magnitude of completeness (Mc) and its spatial variations are outlined. Significant changes in reporting were found during early 1987, mid 1992, and early 1997. By inspecting the bulletins for 1987 to 1992 we found that the rate of located to recorded events was close to 50%. Comparing cumulative and non cumulative rates for 1987-1992.4 with 1992.4 – 1997.11 there is a difference of about of 60% in the trends of located events. The difference is greater in the region of maximum resolution of the network. The change for the period 1992.4 – 1997.11 as compared to 1997.11 to 2001.5 does not warrant a correction; however the number of events with duration magnitude M ≤3.5 reported during the most recent interval is 38% larger than for the preceding period. Magnitudes calculated by RESNOM (Md) and PDE (m) match if the magnitudes reported by RESNOM are increased by 0.1. The same correction should be applied when merging data from RESNOM with SSN. The minimum magnitude of completeness for current reporting is 2.4. Some areas with good coverage in particular around 32N y 116.5W can detect magnitudes as low as 1.6. The resolution of the network in some areas has improved considerably; with Mc decreasing as much as 1 magnitude unite.