After downloading the Enhanced Edition, go to

Steam > SteamApps > Common > Space Hulk Deathwing - Enhanced Edition > SpaceHulkGame > Binaries > Win64 > SSR

and run "SHDWStatsRetriever.exe" to recover your saves, achievements, stats and special missions maps unlock status.
Unfortunately this needs the files from the old versions to work, so if you uninstalled it already you will need to re-download it before running the tool.

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