Its so weird to hear of people in other countries not being able to finish ANY of the puzzles. Like I've said before, it all depends on where you are, and the 3DS was of course made by Nintendo, a Japanese company, and being in Japan is a very different experience when you own one.
For example, I have every single puzzle finished, and I have had them finished since November. The last pair of puzzles came out on the 8th of November, and by the 10th I was finished with the Kirby puzzle, and I had finished the Doubutsu no Mori (Animal Crossing) puzzle by the 15. I was visiting Shinjuku the day after the Kirby puzzle came out, and I got all the pink pieces halfway through my trip there. In Japan there is such a large amount of people with 3DSs, and since the amount of people in the center of Tokyo is so large, if there's even half of a 40 piece puzzle that has pink pieces, I would say you can finish the entire thing within a few hours of walking around unless you constantly check your system, and travel around the entertainment districts, in which case you can finish it even quicker.
It took me a few extra days to finish the Animal Crossing puzzles since I wasn't traveling, and I live in a rather countryside seaside town about 2 hours from Tokyo, but even with that I finished the puzzle in about a week. So please, don't blame Nintendo for the system in which the puzzles come out. If anything, regions outside of Japan should have had a different system for getting the pink pieces, but in Japan you can finish it really quickly even if you live in a really out of the way area.
So, for me, I've had the puzzles finished for about 2 and a half months, and am sitting here waiting for a new one since the middle of November.


