Well, Crivs, do I have a treat for you! No, that isn't a question, it's a statement, as I'm now about to unleash on you the Gold Key comic strip adaptation of The Man Called Flintstone movie from 1966 - including some clips from the film itself. See if you can spot the apparent plot flaw that tends to suggest not a lot of thought was put into the story. Either that or Hanna-Barbera's writers were making some of it up as they went along. Don't worry if it passes over your head, I'll spell it out at the foot of the post. Enjoy!
(Update: Since first publishing this post, I've obtained a better copy of the comic without the 'ripples' the first one had. I've therefore rescanned the complete story and replaced the images with better ones. Well done me.)
And now - the plot flaw. As Triple X is the Green Goose, he clearly would've known that Fred was standing in for Rock Slag and be therefore unable to supply him with the information he was looking for. Which, as he was a government agent himself on the same case, he wouldn't have had to look for as he'd surely have known from the beginning when the Chief gave him his mission instructions. H-B didn't think it through, did they?
Or maybe they did. I've just noticed the Chief introduces Fred to Triple X as Rock Slag, not Flintstone, so maybe X/Goose didn't know Fred was a stand-in. However, he'd surely have known the overall details of the case he (Triple X) was on, going by what his mission instructions were, and just what info the Chief and Slag were looking for about his criminal alter-ego.