When did LEGO Minifigure Leg mold designs change?

Question

I am trying to identify the changeover dates for different minifigure leg molds. e.g. a figure from 1978 has no visible seams on the legs figures from the late 1980s have visible seams, but it might be earlier a figure from 2018 has visible seams on the outside of each leg the leg, and ©LEGO imprinted under the toe. It sees to have happened after 2012

The legs with seams have a marginally larger hole in the base for studs, and so are easier to attach/remove to/from an attached plate than the older ones.

Does anyone know when these molds changed over more accurately ?

Answer 1

Further investigation reveals that 2013 was when the word '©LEGO' started to appear under the minifigure 'toes' I am still unsure about the first appearance of seams in the leg molds