I am confused that what is the difference between controllers modifications in the storage directory and the catalog directory.
Editions in extensions don't affect pages in catalog controllers.
Can you enlight me?
When you see a core file in storage/modification folder, it means that you have an OCMod file that needs to edit that core file. for example:
Core File (OpenCart original file):
catalog/controller/product/product.php
Modification File (copy of original file with some edits altered by OCMod):
storage/modification/catalog/controller/product/product.php
Go to admin panel / Extensions / Modifications, you should see a list of installed OCMod files. also you can see a Refresh button on top of this page, if you hit this button all files in storage/modification folder will be deleted And if necessary, it will be rebuilt.
Read more about modification system: https://github.com/opencart/opencart/wiki/Modification-System