I went through a period with a lot of what I cal "re-dreaming". I believe it was because I was training my recall at the time. I went so far as to use mantras telling myself to remember my dreams, even the early ones in the night. As a result, I would either have another dream later of telling the earlier dream to someone, or I would just dream it again but with differences.

As with pulling up any memory, it actually gets changed with the recalling, because of any emotions or associations that new get attached to it - along with whatever new random elements get attached. This is actually known about memory - it isn't just a simple matter of 'remembering' something exactly as it happened, but it's distorted because your memory isn't perfect, and it gets mixed in with any new content that's strong on your mind at the time of recalling. In other words each time you remember something you subtlely change it. Sometimes not so subtly. Just as if you "do the same thing" every day after some time it will have changed somewhat, maybe without your even realizing it.

Often I find that the re-dreamed versions get more cartoonish or messed up, and they make it really hard to remember the earlier versions. Ive occasionally dreamed something 3 or maybe 4 times in a night. And understandably, they all get mixed up together and hard to untangle.

Recently though it happened again and I suspect in this case the re-dreaming was actually a better clarification of the themes of the original dream. Possibly because now I'm making a good effort to interpret and understand the meaning of my dreams.