The waves kept coming out on a regular schedule - January 17, then March 13 (two months later), then May 24 (a little over two months), then August 23 (three months). Even if Wave 5 took as long to come out as Wave 4, shouldn't it be available by now? It would be extremely frustrating if the set were not completed…

Somebody observed that each monster had a corresponding number, and that the monsters generally increased in number following the release of the sets. If you organized these numbers in ascending order, there were a couple of holes (missing numbers). It was speculated that the Nightgaunt was one such missing number, so it might be reasonable to conclude that there might have been a printing mishap with certain monsters along the way that need to get repaired, and that this abnormal release delay might be reflective of that.

I'd like to get some info on this as well.

Because of the lack of info from FFG i have actually started buying minis for the missing monsters. There are quite good ones out there.