"The Label Code (LC) was introduced in 1977 by the IFPI (International Federation of Phonogram and Videogram Industries) in order to unmistakably identify the different record labels (see Introduction, Record labels) for rights purposes. The Label Code consists historically of 4 figures, presently being extended to 5 figures, preceded by LC and a dash (e.g. LC-0193 = Electrola; LC-0233 = His Master's Voice). Note that the number of countries using the LC is limited, and that the code given on the item is not always accurate." 
When entering a label code in MusicBrainz, use only the numerical part, with or without leading zeros, which is the only relevant part stored in the database.
Note that subsidiaries do not necessarily have an independent label code, and may just use the label code of their parent label.
Also note that entering a label with label code that is already in use in MusicBrainz requires you to add a disambiguation comment.
- https://labelrecherche.gvl.de/ (German)
Please treat these lists with care, they are unofficial. Don't use them as sole reference!