You see, it all depends on the situation you are in. If you are preparing for an organ recital and you have some 9 or 10 organ pieces then you have to find a way to practice all of them from time to time. But if you are playing organ just for fun, it is probably more beneficial to you, if you could practice just a few pieces at a time. Let me explain why is it so.
The thing is that every fragment of your piece, every combination of 2 and 3 voices requires at least 3 correct repetitions to successfully master it. I would say that even playing solo voices at least 3 times in a row correctly is a very first step. And all of this has to be done in a slow tempo.
Then the answer to the question about wide vs deep practice is quite clear. If you have time in your day to practice many pieces at the deep level like I described above, then of course you can play 9 or 10 of them in one practice session.
But be aware that this kind of practice would require at least 4 hours a day of your time. Not everyone has this kind of perseverance, right? Plus we all have other different responsibilities during the day.
So what is the best solution in this situation?
I suggest subdividing your entire program into blocks of 3 or 4 compositions. Then practice one block on Monday, Wednesday, and Friday, and leave the rest of the program for Tuesday, Thursday, and Saturday. In other words, you can alternate the two parts of your program so that you can easily practice them on a deeper level in each practice session.
Note that here I don't mean the sight-reading practice. The sight-reading should be done by playing new and unfamiliar compositions once or twice in a systematic manner. By practicing sight-reading, you don't need to master each piece and play it many times correctly. But with practicing organ repertoire, deep practice is much better than wide practice.
If you are preparing for an organ recital, then playing the entire program occasionally is also necessary. This will give you the required stamina and endurance to perform a long program without breaks.
Use this advice in your organ practice today. Try to go deep and you will begin to notice some tremendous improvement in your pieces and your technique in a matter of just a few weeks.
By the way, do you want to learn my special powerful techniques which help me to master any piece of organ music up to 10 times faster? If so, download my free Organ Practice Guide.
Or if you really want to learn to play any organ composition at sight fluently and without mistakes while working only 15 minutes a day, check out my systematic master course in Organ Sight-Reading.