In this case, the Four Seasons would be intuitively a collection to me, rather than a work, as well as Il cimento dell’armonia e dell’inventione. Each concerto is a work, and the four concertos would be part of two collections.
The Four Seasons and Il cimento… both respects the definition of a collection (I cite reosarevok from here):
Collection (Y part of collection: X, X collects: Y): wording could be changed but basically this would represent a case where the “parent work” is not necessarily meant to be performed as a set. For example, Brahms’ collection of 5 songs, op. 72, or Debussy’s second book of preludes, or Beethoven’s 3 piano sonatas, op. 10. Parts of a collection can still be ordered/numbered (and often are!) - it just doesn’t necessarily refer to the required performance order.