Recently, I've been acquiring a few volumes in Leslie Klinger's annotated version of the Holmes canon entitled The Sherlock Holmes Reference Library. (I did a post on this collection a couple weeks ago.) I encountered a little problem with a third party Amazon seller when I ordered The Sign of Four, that I think demonstrates one challenge that can make public domain works so tricky in this modern world.
A simple Amazon search will find all kinds of editions of Sherlock Holmes very quickly. The problem is, the description of any individual volume does not always match the edition for which you are searching. When I ordered the Klinger edition of The Sign of Four, it showed not only a picture that matched that edition, but even had the correct publication number, including ISBN. Imagine my surprise, then, when I received a very small, cheap reprint with absolutely no annotations. I finally got the situation worked out, but ended up having to order a new copy for several dollars more. I've noticed a similar problem in the past when I was trying to find individual volumes of The Oxford Sherlock Holmes. What you search for doesn't always match what comes up. I've also experienced similar confusion with versions of Shakespeare (another public domain classic).
The thing with public domains works is, anyone can reprint them and sell them at a pretty good profit. And there's little in the way of control of information that is available from online booksellers (Amazon isn't the only seller with whom I've experienced this problem in the past). So if you're looking for Sherlock Holmes editions on the Internet, be as careful as you can to be sure you're ordering the right one. Sometimes, even when all the info matches, you still get the wrong one, as I did with The Sign of Four. Don't get me wrong, I am very pleased that it is so easy to find books online, but with public domain works, there are some unique challenges. Happy shopping!
I'm a stay-at-home dad, and Director of Music Ministries at a United Methodist Church in Mt. Juliet, TN. And a longtime fan of Sherlock Holmes.