I can't seem to find when the start date was when Disney began serializing or stamping the lot number on the back of pins. Does anyone know? I wouldn't say they are serial numbers as some pins share the same number, but rather it must be a lot number of sorts.

The reason I ask is because I have a Splash Mountain pin dated 2008 with a lot number stamp on the back. I wouldn't think the lot number stamping had started back in 2008, but this pin looks and feels like it's authentic.

I've seen some newer pins, like hidden mickeys and such, that do not have the number stamp even as new as 2013/2014, so I don't think every pin gets the serial/lot number.

Can anyone shed some light on this?

Thanks!