I've just had a look today, using the free desktop version. Two of the albums mentioned above (Silly Sisters and Early Days) are visible to me. I haven't looked further.

Spotify have a problem with low-streaming tracks. They have now stopped paying for streams which don't meet a monthly threshold, on the basis that they don't generate much income, and this never reaches the artist anyway. This last excuse doesn't wash - either they don't understand how music aggregators work or they are trying to pull the wool over our eyes. However they seem happy to still take punters' money to listen to these tracks.