I have just been trialling the Series function which is a great feature.
I have also discovered a bit of problem. In the example of collections which only have an Edition Group, there is no way of adding them to the Series.
An example is The Thirteen Problems (1932) by Agatha Christie which uses a framing device to connect the various short stories. The stories all feature Miss Marple: The Thirteen Problems (EditionGroup) – BookBrainz
On Goodreads the collection The Thirteen Problems is given the number 1.1 of the Miss Marple series: https://www.goodreads.com/series/51798-miss-marple
The only work around that I can think of is numbering the various short stories in the collection, which have their own Work, as 1.1, 1.2, etc.