which one to add mine to?

https://www.librarything.com/search.php?search=great+cases+of+sherlock+holmes%2C...

Description in first one listed: "the twelve short stories that made up . . ." Mine has 20 short stories. "the most popular novel, THE HOUND OF THE BASKERVILLES", not included in my book.
Mine: "The Franklin Library of Mystery Masterpieces" "Great cases of Sherlock Holmes" illustrated by Mitchell Hooks, no ISBN or any other number. Does have copyright dates.

The bast place to start is the add books page. Once you have added the book, you may decide that you need to move it from one work to another. Using the work page shortcut won't give you as much choice about what edition is added, and is also no guarantee as to what work it will end up in.

Given that the vast majority of the 'editions' in the works do not have ISBNs it would be impossible to separate the ones with Hounds from those without.

That was my plan. I had just wanted an opinion from those more knowledgeable. I'm also going to list the short stories included in the "My description" field.
I'm in the process of adding classics and have feeling I'll be encountering this issue more often. I know a book by Poe has the same issue.

Remember that anything you add at the work llevel can be deleted or changed by others who disagree with it.

You might be better of by adding a disambiguation notice that the work seems to include copies with and without The Hound of the Baskervilles.