Spending any time in the music world will make you realize that there is an abundance of editions out there, especially for standard repertoire. Our teachers guide us on which edition to purchase/download. Our orchestra librarians make sure that the correct music is distributed to our folders.
But what about mixing editions? What if you don't want your pianist to borrow your prized copy of the Hummel Trumpet Concerto? You bought an E trumpet for this performance and your music is in E major. You tell your pianist to download it from IMSLP. She has only played it in E-flat and assumes that you will, too. You meet for the first rehearsal and your music is in two different keys! Obviously, there was a miscommunication. If the orchestra parts were in the wrong key, it would have been an even bigger mess. This happens to a greater or lesser degree to all of us
I know of a recording on a major label where the cello soloist plays a composed version of a concerto and the orchestra plays the original version; to someone who knows the piece, it sounds like a mess. When I lived in Detroit, I spent a lot of time at Luck's Music Library. I once asked them why they don't sell Haydn's Concerto No. 5 in C major (this was before I knew that it was a musical hoax by Popper). They told me that people would purchase it by accident instead of the famous C-major concerto. In that case, those 2 concertos had nothing to do with each other besides being in the same key. But this often happens with different editions of the same piece.
Dvořák - Cello Concerto in B minor
This is the simplest case on my list. The reprinted Simrock parts (Kalmus/Luck's) have rehearsal numbers, as does Bärenreiter. But for some reason, Breitkopf Urtext decided to use rehearsal letters. This means that anytime your solo part says 1-2-3, the Breitkopf says A-B-C. The Breitkopf Urtext edition is good, but using the orchestra parts might pose a slight inconvenience.
Haydn - Cello Concerto in D major
Haydn's D-major Concerto is notorious for mismatched parts. There are 2 main versions for the orchestra parts, the original and the "Gevaert" version (orchestrated from Servais's version). Usually, the 2 versions are marked as such. The number of versions for cello and piano is much greater. There are editions with cuts, interpolations, and pitch alterations. Before your first rehearsal, you will want to make sure that the solo part you plan to play matches the accompaniment. Don't assume the pianist/conductor will acquire the correct version.
Miklos Perenyi - Original, without any alterations to the solo part
Daniil Shafran - Traditional Gevaert version (double woodwinds) with the cadenza by Gevaert (most likely Servais)
Christine Walevska - Altered Gevaert version (2 oboes/2 horns), currently available from Breitkopf
CPE Bach - Cello Concertos in A minor and A major
If you get the Breitkopf (Grützmacher) edition of CPE Bach's A-minor concerto, it won't be compatible with the original version's orchestra parts, as you can hear in the (mixed-edition) Tim Hugh (Naxos) recording. The story of the A-major concerto is almost as complicated as that of the Haydn concerto. The editions prepared by Pollein and Cassadó are incompatible with the original orchestra parts. Cassadó's version is altogether in a different key of F major.
Boccherini - Cello Concertos in B-flat major and D major (G. 479)
Boccherini's B-flat major concerto is surrounded by confusion. Someone decided to assign the G. 482 catalog number to the Grützmacher concerto, aka by Boccherini, which is entirely a different piece from Boccherini's G. 482 concerto. Grützmacher did a paste job with 4 of Boccherini's concertos and a Dotzauer etude. The solo parts and orchestra parts are completely incompatible.
Another famous Boccherini concerto, G. 479, has been arranged and reorchestrated by Aslamazyan, Cassadó, Respighi, and others. The solo parts and orchestra parts are incompatible with the original version.
Tchaikovsky - Rococo Variations
These days, more cellists are playing the "original" version of Tchaikovsky's Rococo Variations, but there is not one original version. Among orchestra versions, Luck's sells one reconstructed version. Schott sells another reconstructed version which is incompatible with Luck's. There are 2 unreconstructed original versions, a 1970s Soviet edition (not Kubatsky) and my YL Edition. The latter 2 are compatible. But if you purchase the Peters Urtext or Schott editions, they will be incompatible. Maybe then you might realize that there is nothing wrong with continuing to play the "Fitzenhagen" version. Are you confused yet?
Steven Isserlis - Original, based on the manuscript sources (1970s Soviet edition and YL Edition)
Johannes Moser - Reconstructed version by Kubatsky (Kubatsky/Schott)
Miklos Perenyi - Original, based on the manuscript sources (1970s Soviet edition/YL Edition)
Raphael Wallfisch - Reconstructed version by Kubatsky with additional alteration by Stogorky (Luck's/Kalmus)
Kraft - Cello Concerto, Op. 4
In my exploration of the lesser-played cello repertoire, I've also found the Dominis edition of Antonin Kraft's C-major concerto, Op. 4 not to be compatible with the original version. The Dominis edition has truncated the piece as well as changed the key of the slow movement from E to A major. There are no recordings of the Dominis edition.
Romberg - Cello Concertos
Solo parts from Peters (Grützmacher), Litolff (Schoeder), Carl Fischer (Malkin), and IMC (Rose) editions of Romberg's cello concertos are not compatible with the original orchestra parts.
Bartok - Viola Concerto (cello version)
If you want to play Bartok's Viola Concerto on the cello like Janos Starker, you will need to get the orchestra parts to the Tibor Serly version. The Peter Bartok version parts are incompatible.
The rule of thumb is to try to play from the same edition as the other members of your group. You will save time asking, "Where is letter X?" Number your measures, check the score for inconsistencies in your part and you will be in great shape. If you play in an orchestra and you have a great librarian you can trust that most of the inconsistencies have been smoothed out.