[schapplm]

The solution for the IMDB number issue was not so complicated after all. A fix is rolled out right now.
I set the behavior of the addon to ignore all media with inconsistent data.
This includes movies, episodes and TV shows that do not have a field "uniqueid" in the video database.
In my case this concerns media scraped years ago. You will see this in the log file (debug verbosity) with lines like this:

Code:

get_watched_xbmc: tv show "Rick and Morty" has no tvdb-number in database. tvshowid=217. Unique IDs: ['unknown']. Try rescraping.
get_watched_xbmc: Movie The Green Hornet (2011) has no imdb-number in database. movieid=1972. IDs are ['unknown']. Try rescraping
get_watched_xbmc: tvshow 217 has no tvdb-number. Skipping episode id 17083 (Rick and Morty S01E01)

Rescraping the library solves this. It might be necessary to change the scraper of a directory to force all media to be rescraped.
You can also check your database using the JSON commands that are also used in the addon. For this you need to enable the web interface. My example is with port 6111 which you might adapt to your settings.

Code:

http://localhost:61111/jsonrpc?request={ "jsonrpc": "2.0", "method": "VideoLibrary.GetTVShows", "params": { "properties":  ["title", "uniqueid"],  "sort": {"order": "ascending", "method": "title"}}, "id": 1 }
http://localhost:61111/jsonrpc?request={ "jsonrpc": "2.0", "method": "VideoLibrary.GetMovies", "params": { "properties":  ["title", "year", "lastplayed", "playcount", "uniqueid"],  "sort": {"order": "ascending", "method": "title"}}, "id": 1 }
http://localhost:61111/jsonrpc?request={ "jsonrpc": "2.0", "method": "VideoLibrary.GetEpisodes", "params": { "properties":  ["tvshowid", "season", "episode", "playcount", "showtitle", "lastplayed", "uniqueid"]}, "id": 1 }

The fields in uniqueid now contain all possible sources, i.e. all three of imdb, tvdb, tmdb for the TV shows.