Rewriting by accident...
(LOS ANGELES, CA)
Question: How do you remember that you had already wrote a paragraph, and you write it again, until you are editing and see the mistake?
Answer: Most of the time, you just hope to catch this type of error in the editing process.
The only other option is to regularly review your work as you write. For instance, you might begin each writing session by reading over what you wrote in the last session, and doing a little editing/revising at that time. Some people don't like doing this, however, because it slows the writing down.
It is probably inevitable that little errors will creep into a manuscript. Sometimes you forget what you wrote earlier and accidentally change a character's eye color or some similar detail later. (It helps to have a separate notebook on such details to refer to.)
Sometimes something is mentioned twice in your manuscript, and when you revise it later, you only revise the first instance and forget about the second. This creates what I call a "ghost of a past version." Sometimes these ghosts refer to old subplots that were abandoned, or plot twists that were changed, characters you meant to do something with and didn't, clues you changed your mind about, etc.
You really need a good editor who can spot continuity errors. You can also get friends to read through your work. Often, they can catch continuity errors you don't because you have a tendency to skim through sections you think you know too well.
Unfortunately, there are certain errors that only you can spot because only you know what's a ghost and what isn't, what you meant to change but forgot to.
It takes many eyes to catch everything.