"How much weight does a good reference from your URNU CO carry at AIB?"
In my old role as CW officer I attended an AIB as an observer about 3 years ago. The board will look at the reports briefly, but more to provide background and give a chance to let them know what questions to ask. All the assessment is based on performance on the day and not prior experience.
I was impressed at how fair the system is, and how much they do want the candidates to pass!