When I first started my company I half assed it. The LLC was quick and the EIN took two weeks. I accidentally signed a contract with my name instead of the company and elected to be a sole proprietorship. These are all the worst ways tax-wise to do this.

By Nov that year I decided to look into the tax implications and they were unpleasant so I wrote the IRS asking to be considered an S corp from the beginning of the year and they sent me a letter saying it was so. I ran payroll in Dec to catch up.

When doing taxes likewise I added a cover letter explaining the mistake about which entity was to receive the money and then assigned the income to the S corp on the return and worked everything through and corrected it in the right way.

The return took months to process and I had a mistake in the taxes that I was fined for a couple thousand which was reasonable but they accepted all these natural errors that I fixed up.

That sequence of encounters with the US government blew my mind. The much maligned IRS was eminently reasonable.