In the 'Type Coverage Checker' tool, there's an error where, when selecting the 'Old Type Chart' feature, Pokémon that are Fairy-type from Gen VI onwards lose their Fairy-type. For example, Togepi, which should be Normal-type, acts as typeless, while Togetic becomes pure Flying-type instead of Normal/Flying. I've discovered this by enabling the feature and selecting all types, in which all pure Fairy-types are placed in the Normal effectiveness tab, even the ones that were pure Normal before Gen VI.
Edit: Just thought of a solution, remove Fairy type if the mon is dual-type (e.g. Mawile Steel/Fairy -> Steel, Azurill Normal/Fairy -> Normal) and replace Fairy with Normal if the mon is pure Fairy (e.g. Cleffa Fairy -> Normal), hope that helps (and is possible).