Filmspeeds for common reverse Super 8 films are mostly marked for artificial light (without wratten filter - 85). For daylight you must use this filter, which reduces the amount of light passing onto the film surface. This is the reason why the same film “has different filmspeeds”.
A Kodak Kodachrome40 has 40 ASA in artificial light (without Wratten filter) and 25 ASA in daylight. This means for usage, in daylight the f-stop must be 2/3 more open.
A Kodak Ektachrome 64T film (artificial / Tungsten) used without Wratten filter 85B has 64 ASA. Used with Wratten 85B for dayligth usage it has only 40 ASA. Also for this film the f-stop must be 2/3 more open in daylight...