What is the value of a world book encyclopedia set with child craft books with world book year books 1970-1978?
Sorry to break this to you, but effectively nothing.
Encyclopedia sets are often quite expensive, so people are
reluctant to throw them away when they become outdated. You'll find
a lot of old encyclopedia sets at library book sales, generally for
about 25 cents per volume, because someone donated them and the
library has no use for them since they're out of date.
It's true that much of the information is probably the same as
in the current set, but the catch is that if you knew which
information was still current, you wouldn't need the encyclopedia
in the first place.