I'm old enough to know that "bold-faced" is recent usage. Here's information cribbed from a couple of sources:
The original term seems to have been bald-faced (bare-faced) and refers to a face without whiskers. Beards were commonly worn by businessmen in the 18th and 19th century as an attempt to mask facial expressions when making business deals. Thus a bald-faced liar was not a very good liar, and was not able to lie without the guilt showing on his face.
It's just the last 5 years or so that "bold" has come into usage. It refers to a typeface. It is used metaphorically in speech. In the same way that a typesetter uses bold face type to highlight specific text and set it apart, a bold face lie stands out in such a way as to not be mistaken for the truth.
Thank you !