I do not see any evidence of wrongdoing here. A traveler going nonrev will automatically show up on the list as a Thru in the connection city once they are given a seat in the upline or origin city. Sabre is supposed to do this automatically once the seat is assigned. Just because they were given a seat the day before for the first flight is not a violation. Sometimes if flights are very empty the flight will be set to automatically accommodate nonrevs at a certain priority code or higher. On empty flights this is often set to D1 and higher and is something Sabre can do on its own.
This means that a nonrev checking in D1 or higher would automatically be given a seat out of DTW and then appear on the list on ORD as a D1T. Now if a flight cancels the next day and the seat is revoked and the nonrev does not make the flight, they will still show on the list on ORD until their name is called and they are listed as 'No Answer' or they cancel the PNR, or if the agent in ORD is not too busy they might look to see that the nonrev ended up not making the flight, but they usually don't have time and type 'No Answer' or 'NOANS'.
If you did not look at the G* for the flight out of DTW then there is no way we would know what the original flight was restricted to. That is the term that is used. If it is set to D1 or higher then it is restricted to D1's and other nonrevs will be accommodated at the gate if a seat is available.
But to answer your question, it is very possible for a Nonrev, especially a D1, to show as Thru at a connection city, even on a domestic connection the day before.
This actually used to happen a lot more for seats in economy. Flights were less restricted in the past and often you got a seat, usually a window, when you checked in for an empty flight on Jetnet. They have evidently gotten more strict about restrictions as I usually do not see any flight unrestricted for D1's or lower for economy. First and Business are always restricted well above the Nonrev level.
If you have Sabre access and the GDSPLY key word in your RES Profile, you can access the G Display for any AA or Envoy flight by using the G* Entry. I hope this helps explain the situation.
You should always hold onto your boarding passes btw. I know of a recent situation where a traveler was connecting in MIA to GRU and had his boarding pass from his origin city and his priority verification for the MIA GRU flight and Sabre never put him on the list for the MIA GRU as a Thru. He was able to show his original boarding pass and priority card and the agent put him on the list for the MIA GRU Flight as a Thru. Although the agent could have just checked the Priority List from the Original Flight, it is usually easier when you have pieces of paper and can say I just got off this flight and I am connecting but I am not on the list for the next flight.
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