A general philosophy behind many countries' requirements for logging training hours is that you cannot log the same hour in the air towards two qualifications.
For example, it the syllabus says "must do 30 hrs x-country for a CPL", and elsewhere "must do 5 hrs x-country by night for a CPL night rating", you can't do 25 hrs by day and 5 hrs by night and claim a CPL with night privileges. In my example you probably could claim a CPL (provided all of the 25+5 hrs met all relevant law, including appropriately rated instructor), but you'd have to do another 5 hrs by night to get night privileges.
There are exceptions of course, but they are usually specifically mentioned in the law books.
hope this helps to fill in the background to your question.
O8