Since I'm editing on Wikisources (<2 years) I look at the statistics and notice that the stats (article Count) for different languages are counted in different ways. For example, for en and fr ws the number of articles comprises pages in the Main namespace (without redirs) and also Page, Author and Index Namespaces (for en ws: approx. 500k in main and 1.1 mln in Author, Page, and Index ) - but for pl, it and others ws, article Count covers only the main namespace (for pl ws only ~100k, excluding ~350k in Page ns).
It took me some time to find the cause in Wikistats code... and:
the problem is that at line 47 of WikiCountsInput.pm file there are list of ws namespaces that are counted. Namespaces 102, 104 and 106 these are Author, Page and Index NS for en and fr ws, but they are not fixed for all sources - for pl ws Author, Page and Index -> 104, 100, and 102, for it ws -> 102, 108 and 110, etc. for others...
Thus, the current pl and it ws Stats results are very understated compared to en and fr. This situation is "unfair" because the most of the Wikisource content is in Page ns.
Could you modify the code of Wikistats to identify ws content namespaces by their canonical name or add the correct numbers for pl and it ws?