Page for artist 'John Williams' has two different artists: John Williams classical guitarist (Australian), and composer John Williams (American). Albums are totally mixed up.
The same with John Powell: John Powell British film composer, and John Powell American pianist and composer. I suppose there are some other confusions, but this is which I noticed right away.
There are also albums not attributed to any composer, although they should be.
In general, there is a great confusion with composers of film music: there is always section of albums attributed to a given composer, and a section of albums 'appears on'. While in case of film scores there is very often a situation when on the album you will find songs of different artists, the whole album is usually entitled 'composed by' or 'music by', what means that such album should be attributed to the given composer as one of his/her main works. Otherwise it is very confusing, and one has to search through endless lists of 'appears on' to find well-known albums of well-known composers. This should be sorted out, I think.
Apparently, there is no one much concerned with right order and attribution of film music albums on Spotify. If you need more detailed information or any help, please let me know :)
Otherwise, Spotify is a great resource of finding music, although it seems that there are very strange omissions in terms of film music, what perhaps is the result of copyright agreements. Hopfully your library will be updated in time.