Thanks for the links, and sorry to be a pain, but even after having RTFM, there seems to be no discussion on the limitations of showing caches with difficulty level of 3 and above. Multi, mystery, etc. I am aware of, but I didn't read anything about the caches difficulties.
Checking back on a couple of my other finds I see that I must have "adapted in the field" to find them as I hadn't twigged earlier.
And if this is the hidden message that Groundspeak have applied to the Intro App, then I think I finally understand why so many long-time cachers are so dismissive of the newer "app only" cachers.