At what date did Lego start stamping minifigure feet?

uterbrauten · 2014-07-10T15:24:08.000Z

I was wondering when this started. Specifically, I have been buying what I was told were authentic Batman and related minifigures off of ebay. I have had no real reason to doubt anything until I got 2 from the same year: a 2006 Gray/Black Batman, and a 2006 Nightwing. The Batman does not have a foot stamp, but Nightwing does. I'm wondering if the Batman legs are not genuine, or if the Nightwing ones were newer legs added to an older torso (or a counterfiet one). Does anyone have any info on when this practice started, and/or if all authentic parts have a stamp (or if it depends on location of production)? Thanks.