That is why I am surprised, it seems to me phone records of such people would have been checked or at least they would have been aware of them.
I still think it could easily be someone we are well aware of. Someone could have easily had a pre paid phone they didn't know about. Even PAIGE might have had one.
If you have a regular Sprint/Verizon whatever phone, sure they will pull those records. If they search your house, sure they will look for another phone. If they don't find one then they have no real reason to suspect you have another phone.
Yet, in some cases the people do. "Throw away phones" are a rather common thing. Much easier to buy them anonymously with cash, rotate through them quickly, dispose of them more efficiently and hide them from LE for longer.
If someone recently came to LE with a phone number that someone called them from, or LE recently found the source of a previously unknown number, then LE realized it was another cell phone they were unaware of.... that could explain this.
It also could be that it took time to get the records because they had no reason to request them.
We will have to see... but after seeing the common usage of these phones lately... I wouldn't be surprised if that is what happened here. Then again, not much would surprise me at all.