Please, update category counters in plwikisource by running populateCategory.php .
As it is well-known problem category counters are sometimes not accurate for large categories (T18036: Number of category members (PAGESINCATEGORY) is inaccurate for large categories).
In mid-2012 we decided to adjust some large category counters by adding manual corrections to them on the pages where the values were used.
However, we found that since that time the difference between real category count and the counter is stable, at least for Category:Indeks (exactly the same difference now as 4,5 years ago).
So we hope the problem leading to this discrepancy is (at least partially) solved and we will get more accurate data without manual corrections (which we would like to drop).
I asked our community for an opinion about this task here: