When using filters with search results, you may occasionally see that the result counts or available filters change before and after filtering.
This is due to the Constructor algorithm's desire to maximize conversion potential for any given set of search results. When there are very few results for a given query and or query and filter combination, the algorithm will broaden its scope to increase recall, result count and conversion opportunities.
For instance, when only a few results are found, the algorithm often applies a broader spell-correction algorithm to expand listings. Consequently, as filters narrow a result set, the algorithm may choose to increase the number of results to provide greater conversion opportunities.