A business was incorporated as an S Corporation in 2008.

In 2008 they filed their taxes as an S Corp. The owner is one person who has 4 contractors that work for him. The owner prepared the incorporation documents themselves and made a mistake once they filed the paperwork. The owner really wanted to be just a sole proprietor corporation and not an S Corp for filing purposes.

However in 2009, 2010, 2011, 2012 the owner filed their taxes as sole proprietor instead of an S Corp but never changed the legal status of there company to a sole proprietor.

Does the owner have to have there tax returns amended for 2009, 2010, 2011, and 2012 and file as a S Corporation?