In a qualified manner, I agree with Zinj and Victor. In day to day life, repetitive memories get compressed, but I believe with the right tools they can be uncompressed and broken down into individual items.
As for revisionist memories, I think that depends on the type of memory involved. If it is 'absolute', e.g., something that has been knowingly and intently committed to memory (like phone number) is unlikely to vary or be lost.
I do have an excellent example of a revised memory. The Mercans among you may not get this.
In the episode of The Goodies: Knutters Knoll, Graeme Garden makes an appearance as a very early badly constructed Cyberman. All the equipment he is wearing is supposed to help him in his new hobby of UFO-spotting, and he was talking in a not-quite falsetto voice.
T: "Why are you talking in that voice?"
G: "The normal voice frequencies can interfere with the equipment. You'll find all UFO-spotters talk like this."
T: "Really? Oh, yes, they do, don't they?"
Years later, I saw a News intereview with a long time train-spotter--and he was speaking in exactly the same way!
My parents never did understand why I spent five minutes rolling around on the floor laughing with tears streaming out my eyes. The original joke had been funny, but with the source exposed, all I could see was Graeme with his outrageous costume and giant headlight looking for UFOs.