Established authors make mistakes to

Do established authors still make the same mistakes they did when they first started?

Not to be discouraging however at times yes they do. Experience does not make anyone immune to mistakes and it's perfectly natural to make them. I've found books from well-known authors to have mistakes in them when they are in bookstores. This is when a good copy-editor or a basic editor makes a world of difference with your writing.

If you learned the wrong way the first time it is hard to break that habit and can stick with you for a life time however knowing this will always help you know what to look for when going back over your written work.

When you're typing or editing fast it is easy to miss some mistakes. It's easy to be thinking of a word and look back realizing the sentence is there while it's either missing the sentiment you were hoping for or simply one word is missing. Oddly enough a common mistake is with typing fast. Instead of writing the word 'who' the word 'how' or 'where' versus 'were' is in its place.

In basic daily life we make mistakes that we know how we should have done something or wished we had done it differently. This is the same with writing. An author may have gained much experience over the years with writing however they are still learning to find craft their skills. Some still have editors; after all it is harder to edit your own stories. Stephen King has to send his off to an editor or he will keep re-writing it until it's no longer what the story was originally intending.

It's always a good idea to read over what you have written to make sure its properly spelled, your thought is getting put across or simply understood and effective. Always have fun and enjoy writing your book, this comes across in your writing and if you do not enjoy what you are doing then then take a break and come back to it. Sometimes this can be a year or even an hour.