Question: Let's say you had a doctoral student who you were main supervisor for {~advisor) throughout their data collection and most of their write-up, but just before they finished they changed to another main supervisor and you became deputy supervisor (you moved to a new institution in another country and they wanted someone close at hand). Let's say you then counted this student on your CV as supervised to completion as main supervisor because this is 90% true and because these CV points are important for things like promotion. The plan if anyone ever called you out on this would be to just explain the situation as it is and say that 90% of the work felt like it justified the claim. The student is in Sweden (where the regulations say students have the right to supervisor change without even having to make a case) and the supervisor is a Lecturer (~associate prof) at a UK university who wants to make Reader (~full prof) some day. Is this a bad idea? What is likely to go wrong?

Answer: 
What could go wrong: 

1. You might not be given a chance to explain it.
2. Once someone realizes you fudged this detail a little, it might call all of the other details in your cv into question.
### tl;dr: Just check the binding regulations.

You're asking the wrong people. Some of us think it's bad, some of us don't. In some universities the criteria are this way, in some - that way.

So just open the administrative/academic/promotion-related regulations for your university or department, and see what it says: What *exactly* is supposed to count for promotions? If the wording is not entirely clear, consult the head of your department.

Now, you might be wondering "Ah, but what if he tells me to change my CV, while in fact the promotion committee would have never looked into it?"

Well, maybe. But:

1. It's unethical to do so.
2. The expectation of benefit/damage over both cases is not high enough for this to be appealing even if you have no ethical scruples (or if you think the promotion process is otherwise unfair).

having said all of the above I must also tell you that: **Look, you didn't supervise that PhD to completion.** What can I say? You just didn't. You had planned to do it; you would have done it, had the circumstances allowed it; you put in most of the effort towards it - sure. But at the end of the day, that's not what happened.