This is a difference I noticed between collections and series while mirroring the trivia artist series which were being removed (74 at least). Many of them were connected to a "parent" series, for example: Artists who died on Flight AF009 was a subseries of Death by Airplane Crash which was a subseries of Death by Vehicle. Another example is by chaban: Music video is the parent collection of Video: Fanmade and a few others.
Keeping this in the collection descriptions is fine too though.