These Time-Life Books came up once
before. There were 33 books
from 1987 to 1991 and the commercials alone have their own following. Skywalker Ranch probably houses many books sourced in the bibliographies, but for a cursory search for MacGuffins they're all one would need. X-Files definitely pillaged them.
There are other books inspired by von Däniken and In Search Of
with just "Mysteries" or "Unknown" in the title. National Geographic of all publishers grabbed the hype way back in 1979
. Readers Digest had at least three books
in the 80s and a series
of 12 in the 90s. Mysteries of the Unexplained is probably the most widely owned and remembered.