Earthquake activity rates estimated in cross-border regions can differ between countries. For example, considering the FCAT or CPTI15 catalogues in the Italian and French Alps, earthquake activity rates can differ from 20 to 80% depending on the magnitude bin. This study aims at answering the following question: how much of the difference in the annual seismicity rates in the Alps cross-border region is due to different methodologies used to compute historical earthquake magnitudes? To answer this question, we built two new historical (pre-1980) parametric earthquake catalogues for this region considering a common post-1980 earthquake catalogue based on the CPTI15. To focus on methodological differences, it was necessary to first build a common macroseismic and instrumental magnitude dataset to calibrate the two methodologies considered, namely Boxer and QUake-MD. We then applied the two methodologies to the same macroseismic dataset to build the two new historical (pre-1980) parametric earthquake catalogues. Finally, we computed earthquake rates for the two catalogues and found them to be statistically similar. This exercise underlines that reducing existing differences in seismic activity rate estimates across border regions will necessarily require a common definition of instrumental magnitudes and a common macroseismic dataset.