What carries over
Every watched episode lands as a check on the show's season tables, with your original watch dates kept where the export has them.
Hearts stay hearts.
TV Time tracked films too: watch dates land in your diary, want-to-watch in your list.
Completed shows arrive marked watched, dated to the day you finished. Mid-way and saved-for-later shows land in your queue to pick back up.
Special episodes stay behind on purpose: catalogs number them differently, and a wrong guess would mark things you never watched. Anything already tracked here is kept. Imports never overwrite.
Which files work
Both kinds of TV Time export work, exactly as you have them. The official GDPR zip from the old data-request portal can be dropped in whole. The series and movies JSON files from the "TV Time Out" browser extension work too, including copies already realigned to TMDB by community fix tools, whose ids the import honors directly. Files are read in your browser; only the matched titles reach your library.
If you didn't export in time
Then the honest answer is that the history is gone, and no app can get it back. Starting over is lighter than it sounds: add the shows you're watching now, queue the ones you keep meaning to start, and the shelf fills back up in an evening.