[Therion] Difference of length in legend and statistics

Hello, Is there a way to display in the legend of a map the total survey length instead of the total maps length? I have a survey where the total cave length shown in the plan legend is smaller than the total length displayed in the statistics (the statistics file is correct and there are no duplicate surveys). I cannot understand where the discrepancy might come from, but I suspect it is related to the maps (I have some surveys that do not appear on the plan and for which there is no .th2 files). Thanks, Martin