If LE found an unlisted phone number on Debbi's hand,
I believe they would have had Debbi call that number from her phone right away. Debbi must have claimed no memory of how it got there. Imo, LE would quickly assume the abductor might have written it on sleeping or impaired Debbi and that the abductor expected Debbi to call when she found her baby missing (possibly regarding ransom). But, of course, Debbi's phones had been stolen (possibly by said abductor). So, LE may have tried to have Debbi call the number from a civilian phone and gotten no answer.
In the meantime, the FBI, imo, would be scouring the internet for that number using their special software (vendor sights, seller sights, registration forms...). When they found it on Craigslist, they had the perfect guise to get the person's address and move in; quick cash for a GPS. LE may have attempted to call Megan's number several times before anyone answered, but when someone did, they hit the jackpot and got an address immediately.
If the number wasn't really on Debbi's hand, but instead obtained from the cell records from phones at the Irwin house (or found during a home search on a piece of paper, on a match book cover, etc...), I think LE woud have gone through the same process outlined above and gotten the same results.
Does Debbi know Megan? Dunno. Does Debbi know any of Megan's housemates? Dunno. Does anyone who had access to the 3 cell phones know Megan? Dunno.
Here's what I think. If Debbi isn't involved, why wouldn't the news about Jersey and then Megan push Jeremy and Debbi into overdrive - get down to the station ASAP, they might have Lisa or know who does!!!??? They'd be at the police station like bats outta hell with their lawyer ready to answer questions about comings and goings that night. Even if Debbi was blacked out when Lisa disappeared, she would be thrilled to learn that local strangers/acquaintances may somehow know what happened to her baby. She would want to try and remember anything about that night and how these two local characters might fit in; she would want her mind probed so that any knowledge she might have repressed could be surfaced, imo. She would want to know everything about these people. If not involved, Debbi would be hopeful that a quasi-couple might be involved as it would statistically increase the likelihood of Lisa being alive. JMO...
Nope, Debbi remains silent. So, she knows these two (or at least knows of them) and either knows they are not at all involved, or that they can implicate Debbi - no need to subject herself to LE. She may fear that Jersey and Megan know more about her than she'd like to admit to LE, imo.
Debbi and Jeremy's lack of action regarding all the hooplah surrounding Jersey and Megan means that Debbi knows what happened (and/or that LE has shown them solid evidence proving that neither Jersey or Megan can be involved). I can see no other reason for the parents not going down to the station for questioning, and no other reason that their PI & lawyers didn't publicly demand answers about Jersey and Megan and focus on them as much as they did the white blob ( and supposed sightings that night). Nope, no focus on Jersey or Megan from Debbi's team; there's a reason for that imo.
And, now, even the PI and the lawyers are silent. I think they've recently learned a few new facts about their clients and need some time to figure out how to spin it.
ALL JMO...