Family listing every single day this week - how to tell if they made it on the flight

So a large family has been listing themselves everyday for a flight I am interested in taking. Yesterday, they checked in -- but after the flight took off they remained "seat unassigned" on the airport standby list despite them having a high enough priory for them to make it (they were s2 and plently of s4 folk made it). I am assuming they just didn't make it to the gate. Today, I noticed after the flight left they all have a seat assignment on the airport standby list -- does that mean they were actually on the flight? Or can you have a seat assignment and never make the flight? Thanks!

Helpful if you would give the city pairs and flight(s) numbers - here is the BIG WORD "Timely".
After 24 hours can't see anything as Delta archives the passenger record flight history.
It used to be that a person with supervisory credentials could look into the history; but
this is not going to happen unless a very serious breach of non-rev conduct happens.

After the fact ???s - were there enough seats for the entire family to get on a flight ?
If not then the family more in likely let junior seniority/pass order take the vacant seats so
the family could travel together.
Now the flight that shows them with seat assignments it would be presumed that they are
onboard "IF" their boarding passes where scanned - also a possibility that the family was
boarded at the last minute rushed onboard skipping the scanning process.
Last ? did the family have more listings for today or other flights ?
Often times a non-rev will list for more than one flight so that the need to make another
listing when remotely away from access to the DeltaNet - TravelNet can be skipped.
Courtesy note - Please cancel all unused listings !
If not the Non-Rev Standby List is skewered with misleading information.
The Airport Standby List is not - this list shows persons rev and non-rev awaiting a seat

Also, you can have a seat assignment and not make theflight. That would happen if you checkedin online, or at a kiosk/ticket counter, and they assigned seats but you nevermade it to the gate. Not sure if theairport standby list removes the seat assignment or not. I am sure it would if they needed the seatfor the next standby person but if there were enough seats for everyone notsure what it would show.

I have been at the gate with a seat assignment and somethingcome up and had to leave, I had no time to inform anyone I was leaving. Once they call your name and you do notrespond they will reassign those seats if needed. Not the best thing to do as it wastes time asthey see you are not boarded, call your name, wait, call your name again, waitthen call the next inline waiting for seats.

As R.M. stated, I have seen people list for multipleflights, lets say ATL-LAX and also ATL-SLC-LAX because the direct flight isiffy and the indirect flight departure time is within 5 or 10 minutes of thedirect flight you would not have time to list yourself if you missed the directflight. You are not supposed to do thisbut in cases like this would you?