star trek - Why was there apparently no knowledge of the missing ship in the Typhon Expanse?

In the TNG episode "Cause and Effect", we are treated to the following line of dialogue...three times.

"Captain's Log, Stardate 45652.1. The Enterprise has entered an area of space known as the Typhon Expanse. We are the first Starfleet vessel to chart this unexplored region."

This strongly suggests that no Starfleet ship has ever actually been into this part of space.

Yet the very end of the episode shows that a Starfleet ship WAS in this section of space, Specifically the USS Bozeman, years ago. Proven when it emerged from a temporal loop just in front of the Enterprise.

How do we account for this inconsistency - saying that the Typhon Expanse has never been charted, and yet there clearly being a federation ship already in the Typhon Expanse?

Answer

Like so many things military, it may have simply been that the Enterprise was the first "official" Starfleet vessel to chart this unexplored region. Since this region was near Klingon space, it is possible there were few, if any, official explorations of Typhon space and none that were on record.

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  Depending on how well known the phenomenon of the Tyhon Expanse was, it may simply have been a region marked by probes and thus known but unexplored.

  
  


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  Remember it was not unexpected for the Federation to scout the borders of their territory unofficially. The TOS Enterprise spent quite a bit of time scouting and even occasionally crossing the Romulan Neutral Zone, unofficially, of course.

  
  


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  The starship, the USS Bozeman was the ship discovered inside of the Typhon Expanse. It was there for ninety years, though from the perspective of the crew inside only a few weeks had passed.

  
  
  


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  The simplest explanation is either the Bozeman was not meant to be in that region and thus it was considered lost and its location was unknown, or there was the possibility of being an off-the-books operation, since Typhon space is near Klingon territory.

  
  


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  Given the Soyuz-class starships were super-destroyers or attack frigate size vessels, it is unlikely it would have been there on a purely scientific mission, it may have been gathering intelligence on Klingon ship movement. The Bozeman was lost in 2278 and the Khitomer Accords aren't signed until 2293, so there may still have been border disputes between the Klingons and Federation during that time.