calendars are not transported individually, it is always the entire table with all calendars that get transported.
Because of that fact some consultants tend to create and change calendars in the production system. (wonder why they do not do the same for account determination, because it is as well transported as complete table). If then another consultant uses the standard way, then it will lead to a total loss of all changes that were done only the production system.
Make sure that you lookup the change log in production, and then do the changes to the correct values in development and transport it again.