Ah, gotchya.
What's the difference between the SS-n-6 and a true SLBM?
Nothing. It's just a really old, really short range one that they got from other places and are using. It's throw weight is really limited, and it's range more so.
So while yes, it's an SLBM, it's utility to them as such is questionable...
Think about it this way:
1. We are -really- good at hunting modern subs
2. We are galactically amazing at hunting shitty subs...except limited range diesel boats in littoral waters
3. The boats we have trouble with can't get close enough to hit us with that type of SLBM
4. If they used SLBMs, they would be taking something rare and valuable to them (compact warheads) and putting them in the easiest place possible for us to wack them.
Hence, my opinion that any push on that front is "hey look what we can do with shiny thing" typical nork behavior. -especially- when it's "take missile we bought from someome and do exactly with it what it has done hundreds of times...except we will fail at it."
So it's more telling they can't make a proven, nearly 50 year old fully vetted and delivered item do what it's supposed to, rather than any risk.
Now, taking that missile and making a better one on a land mobile platform? That's strategically valuable as it keeps their jewels close and protected.