I never give my 2 D. kingianum + 1 hybrid any winter rest and they are doing just fine (the kingianum hybrid is actually starting to bloom!). I actually had the same thing happen to me with a keiki I received from an order (the roots were literally less than half a cm long). It was one of my first plants, so I didn't know anything about winter rest or whatever (I guess I still don't
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). I actually first just put the plant in a cup of water and later actually stuck it in dirt
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where it started growing another shoot before transitioning to a mix of sphagnum moss and bark (moss throughout pot, not just on top). I watered it pretty intensively (roots were always wet) and now it's doing pretty okay. <- I also kept it under high humidity at the time.
hope this helps