I'm not sure of the history of April 15 specifically, but April or so is probably about the earliest you can easily get all your reconciled financial statements

I'm not sure of the history of April 15 specifically, but April or so is probably about the earliest you can easily get all your reconciled financial statements if your finances are at all complex and put together your tax filings. I don't even get a W-2 until late January and I have at least one statement that tends to trail into early March.