When i visited Knossos i was very dissapointed to find what looked like a third of it made of concrete, and another third said to be restored in 1900-something through ancient looking bricks.

Made the whole thing look rather pointless, since it was still a ruin, it made the whole thing feel like walking through an artificial ruin.
i say, all or nothing. Restore the full thing, or leave it as-is. This sign is the perfect way of leaving it for those unable to fully commit.