What he thought he said... If I recall, he doesn't even know which officer he overheard. If the officer on the phone had filed a report that claimed the AV told him there were 20 assailants then you might have something.
If they can find no one from DPD who was at the hospital and fesses up and we have a document from an actual interviewer claiming 20 in attendance, not 20 attackers then, IMO Ofc. Day is discredited somewhat. He may have heard that she has changed her story several times, but he could have mis-heard the part about 20 attackers...
The person on the phone may even have misspoke unknowingly but when they took time to think through a report, transcribed more accurately what they recall.
I will also concede there has been some significant delays in filing reports and some convenient lapses in memory from some key players early in the investigation.
Patrick Baker said it was Sgt. Shelton who Day overheard talking to his watch commander. I find it very odd that Shelton's report wasn't generated until April 9, over three weeks after the party. Perhaps he had detailed notes from that evening, but didn't write them up until later. I hope he wasn't just going on memory, especially since his report wasn't produced until after the IDs were made.
Everything people testify to is what they thought they heard or saw. [Experts aside who give their opinion.] Again, it is admissible that he heard the DPD talking about her claim of 20 assailants, if DPD claims she never changed her story.
Notice he did not hear 20 assailants and tell the University boy this is a huge [or hugh in FR speak] problem. He over heard the discussion of 20 assailants as discrediting her. So he heard this in context. He was sure enough of what he heard to put it down on an incident report [or whatever Duke PD calls their form] and he did not follow up with a correction.
Now I doubt this comes up in trial, but if it were to Nifong could produce both ends of the conversation and try to refute this. But 20 is in the record now, just like 4 strippers with names are in the record, just like Pittman [aka Roberts] being with her all by five minutes and Mangum wanting to go back in and try to make some more money is in the record. Some people will try to claim they did not say what others heard them say at trial. if it ever comes to that. Mangum will likely claim she said she and Roberts [aka Nikki in this context] were sent by Tammy at Angel's and officer Sutton misunderstood her.
DPD did not believe her that night. DPD was never going to refer this case to the DA's office. Nifong saw the political opportunity it was for him and that is why he stepped in and took over the case.