LED bulbs

Just for fun I dismantled my "burned out" LEDs . Took each strip , each with ten smd's hooked them direct to car battery. They all worked !!! Did not use diodes or resistors (whatever they are) from origional . My research showed that "12 v " LEDs will operate at a variable current i.e. 10-15 volts. The higher current will just shorten life expectancy. Cannot understand yet why assembled " bulb" failed