How do you know whether or not 2 different dream scenes are actually 2 different dreams or just one with a scene change? Do scences change in normal dreams? An example
The day before yesterday: I woke up remembering 2 different dream scenes. Here Im not sure if it was two or one.
Yesterday: Woke up and remembered a dream, then went back to bed and remembered another one. Here Im pretty sure it was one.
Does it really matter? I think not.
Well how are you supposed to know how many dreams you remembered then?
Very tricky question, indeed. But think about it, what is the actual difference between a dream and a scene change? In my opinion, there is no difference.
Of course, when you go through the different sleep stages at night, you have several REM periods. And between these there are NREM periods, which marks the ending of one dream and the beginning of another one. So, technically I think you have exactly one dream every REM period. But for the sake of simplicity, I just think of each period in REM that I can not link to any other parts of that same REM period, as a separate dream.
Yes, you can have dreams where the scene will suddenly change. Now if the dream is continuing with the same plot I would count it as one dream. But, if the overall plot changes then I would then count them as 2 separate dreams. That is just what I would do there really is no “rule” about this.
It gets very complicated because you could have one or several dreams in a rem period.
Oddly enough, if you remember a smooth transition between dream scenes, you would probably count it as one dream, but if you forget it, you would count it as two! 
I do that but it is hard to tell sometimes
I usually count a dream as ending when you go into that half-asleep state or have a FA.