I mentioned this in the 1.2.0 thread, but I have a hypothesis on what's happening. Remember when they said that the new resources came with their own narrative events? Yup, some of the Treasure Resources are gated by goodie huts, each with a choice to reveal the resource or receive an immediate reward.
Now if you're a Distant Lands civ, which will your scout pick? You guessed it - the resources aren't special to them, so they'll probably take the quick payoff. Unfortunately that removes the resource from the board; nothing to find, fight over, or capture. Like it never existed in the first place.
It's just a hypothesis, but it does explain how the Treasure Resources would pass superficial testing - they would count as being correctly seeded but become unavailable through the course of the game. And I suspect no one checked the number of resources at the end of the era to see how well they matched with the seeded number.