For unknown reasons(*) , sometimes getting pages in Page ns connected to the respective Index page via https://en.wikisource.org/w/api.php?action=help&modules=query%2Blinks will not return all pages but only a subset.
e.g.:
- for https://en.wikisource.org/wiki/Index:Anne_of_the_Island_(1920).djvu
- https://en.wikisource.org/w/api.php?action=query&prop=links&titles=Index:Anne%20of%20the%20Island%20(1920).djvu&pllimit=500&plnamespace=104
where not all pages in Page ns are returned, as opposite to e.g.:
- for https://en.wikisource.org/wiki/Index:Through_Bolshevik_Russia_-_Snowden_-_1920.djvu
- https://en.wikisource.org/w/api.php?action=query&prop=links&titles=Index:Through%20Bolshevik%20Russia%20-%20Snowden%20-%201920.djvu&pllimit=500&plnamespace=104
(*) there might be something in the IndexPage itself which alters the query, or some caching issue or a problem in the API.