Is HEL-OSL included in the trial yet?
Well, good question - on DY I think it is, I've heard it advertised on board there (but I've only taken DY once on HEL-OSL since CN started, and I could be mistaking an announcement for HBO-only pax to use CN).
As for the list of origins for which checked baggage is included in CN, I cannot find a list on the Avinor website in English or in Norwegian.