According to coverage by Polygon and other outlets, datamined files circulating online appear to include route data and character variants that are not present in the currently released portions of the expansion.
Nintendo publishes Fire Emblem titles and Intelligent Systems is the long-standing developer of the series for Nintendo platforms; DLC for Switch titles is typically distributed through the Nintendo eShop or announced during Nintendo Direct presentations.
What the reports say (journalistic summary)
Polygon reported that files extracted from the game appear to reference four Lords of the Flame routes named Cai, Dietrich, Theodora and Leda.
The datamine reportedly shows multiple character variants for some cast members; cited examples include alternate depictions of Bertrand in youthful or gladiatorial attire.
Another reported find is an alternate depiction of a character called Talimun without his usual clothing.
These items come from data files that have circulated among modding and datamining communities.
Rewritten statement for clarity
Outlets reporting the matter say the game’s internal files include playable route entries for all four Lords of the Flame and list several character variants not visible in released routes.
Those reports also note that some characters referenced in the files have not yet appeared in the playable content available to players.
Confirmed versus unconfirmed information
It is important to distinguish published reporting from official confirmation.
Polygon and other media have reported on the datamine, but Nintendo and Intelligent Systems have not issued statements confirming the content of these files.
The existence of datamined assets has been reported by third parties, but that reporting does not equate to a developer or publisher announcement.
Historically, Nintendo announces significant Fire Emblem DLC and release details through its official channels, including Nintendo Direct streams and the eShop listing.
What this means for players
Players who wish to avoid spoilers should treat datamine reports cautiously and refrain from seeking leaked files.
For authoritative release dates, route confirmations or DLC schedules, consumers should rely on official Nintendo communications.
As always, coverage of this subject will be updated if Nintendo or Intelligent Systems provide verified information.