Ah oke, the confusion for me comes from the fact that +r123435 works when splitting tracks (lookup on tracks), but not when starting the recording.
As a suggestion, I think it would be really nice if the program would correct it automatically, try the string as it is given, add the r if its missing, add the + if nothing is found, add the brackets, etc. Make my life easier

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Either way I'm happy I can use Discogs lookups as it is, my entire record collection is there added perfectly on release number.
Thanks for the help!