I like to hold myself out as the Club expert on registrations; I have done or been involved in many. I have seen all kinds of issues successfully resolved.
I have been involved (but not at the helm) of registering older Harleys. It is true that they were registered by the engine, not the frame. I did many statutory declarations for an unnamed Harley collector to help him get them registered, but all of these were finished motorcycles.
Please report what you learn from ICBC. I will check in with my collector as well. My thoughts are to not worry about it until the end. The risk is a finished bike and then discover .... problems (like it was stolen ...). I am pretty sure you cannot just register a pile of parts. We used to be able to register just a frame, but ICBC has an issue with that now (and I have a way of fixing that also).
Peace & Grease, Dennis