(ED's explanation of why this tile should not be counted
The following text is Eternised Dragon Explanation on why the Invisible tile in Brinstar Fire Fly Room should not be mandatory in Map Completion :
The reasoning behind this and current state of the art is that due to its behavior deviating from tiles that actually can be coloured pink (which this tile cannot, as opposed to every single other map tile part of 100% Map Completion, so that its behavior in this regard is to be classified as the same behavior that is shared among plenty other visitable inbounds aswell as out of bounds black squares), the community never made a decision about it. On the other hand side though, since the tile is inbounds, it is no issue moving through it, and fortunately the fastest strategy to move through this room passes through this tile anyways. Though it is worth noting that the technical implementation of the Map is entirely independent of what tiles fill a given Map tile, so it depends on if one wants a given 100% Map Completion run to be true to the explicit work that was done on the Map implementation back then the way it was done by the game's developers, or ignore this aspect and define this aspect according to inbounds Map tile accessibility reasoning, which might possibly risk requiring a uniform definition on at what accessibility limits a Map tile is or is not to be counted towards the set of tiles that shall be collected.