It is often important to look at the Urtext (original/unedited) version of a composer's work. It is best to use the Collected Works for this. Search in Oxford Music Online to find out the book and volume number, and then use our catalog.
For example, if you are researching Liszt, there are several collections of his compositions:
To review one of his orchestral pieces, see this example:
This piece is available in our collection in volume 1: