people have been doing this for decades. it's for obsessive collectors who want to match up sleeves to their collection. nobody is gonna pay more than a few cents for a common sleeve like spring. also the obsessive collector thing is sort of silly (I still would understand doing it knowing this) because when the records were released a lot of the records were put in whatever sleeve was available at the time, e.g. could have been a plain sleeve, could have been one from a different era, etc.