When trying to identify different editions of the same play, you need to look for both the publisher and the copyright year. Sometimes you will also see an edition note (e.g. Revised ed., 2nd ed.) or the publication will be part of a series/set.
Books and plays that are part of RIT's collection can be found using the library's catalog. Try searching for the title and author of your work using Author/Title search on the catalog's advanced search screen:
Once you've identified any relevant editions in RIT's collection, try expanding your search to other libraries. You can use a similar search strategy to look for editions available through ConnectNY, a consortium of libraries in New York State. Or, try searching WorldCat to search library catalogs worldwide.