The Spotify 'Every UK Number One: 2016' playlist

[Tom_Henderson]

Purely out of interest could anyone explain the methodology behind the Spotify curated (my first ever chance to use this pretentious word 🙂 ) playlist: "Every UK Number One: 2016". I'll leave aside the slight confusion of the main title saying 2016 and the sub-heading saying "of the past year", which is mainly 2015. Anyway, there are 60 tracks listed but if I go to, say, "List of UK Singles Chart number ones" in Wikipedia then the entries for 2015 plus 2016 only come to 30. So, there must be other categories of number ones in the list. What are they?