Totally unreliable and not worth the paper.
Surely its common sense that if COLP was undertaking a proper robust investigation then interviewees need to write their version of events (notes) in their own words/hand and sign accordingly?
You would need to take that up with COLP. I assume they interviewed witnesses one at a time, with a note taker present. Either the actual notes or photocopies of the notes were then retained in storage. Eventually, the notes were disclosed to the defence.
At some point, either upon release or at a later period, the notes would have been entered in to the archive and cross-referencing system used by the CT.