How far along are N. Korea's submarine-launched ballistic missiles?

It's capability is overstated by current reckoning.

Ankit Panda, The Diplomat
11 January 2016
After grabbing headlines the world over on January 6 for its (dubious) claim of having successfully tested a hydrogen bomb, North Korea released what it claimed was video of successful submarine-launched ballistic missile (SLBM) test on Friday. The test was supposedly carried out in late-December 2015. (You can view the full video here.)
Immediately after the video was released, the South Korean military came out and said that the video appeared to have been manipulated. North Korea’s SLBM ejection tests have had trouble in the past. Last year’s test of the KN-11/Bukkeukseong-1 (“Polaris-1”) SLBM was shown to have taken place from an underwater barge, undercutting North Korea’s claim of a successful ejection from its Sinpo-class submarine. In late November, Pyongyang attempted a submarine ejection in earnest that was reported to have failed.
Though the South Korean military is yet to release any sort of definitive evidence that the video was altered, the community of open-source intelligence analysts out there has already gotten hard to work in attempting to prove that the video is less-than-genuine. Notably, the footage released this week does not show any close-ups of the missile unlike the footage from last May, clearly showing the distinctive-looking KN-11 (the missile bears a strong resemblance to the Soviet Union’s R-27/SS-N-6 Serb SLBMs).
Dave Schmerler, a researcher with the James Martin Center for Nonproliferation Studies, spotted that the footage showing the missile breaking through a layer of clouds is from footage of a June 2014 missile launch. Schmerler additionally geolocated the background of the SLBM test video, showing that it had taken place roughly near North Korea’s Sinpo shipyard.
North Korea releases this sort of footage to send a signal. After widespread reporting of the unsuccessful SLBM test in November and discovery of the underwater barge ejection in the case of the May launch, Pyongyang was likely eager to send a signal that its SLBMs were on track. The nuclear test on the 6th got people to take North Korea seriously; releasing this footage shortly thereafter is an attempt to make the SLBM threat stick. (For what its worth, the release of the footage coincided with Kim Jong-un’s birthday.)
If Pyongyang really wants to show the world that it has successfully conducted a full flight test of its KN-11 SLBM from its Sinpo-class submarine, it would do well to release detailed footage like the sort it showed in May. The long-range shots, speedy cuts, and fast editing with this latest release suggest that Pyongyang is furtively trying to get away with overstating the state of its SLBM progress.