In the book of Quantitative Finance by Schmidt, on page five it states:

"Some financial markets are organized in exchanges or bourses (e.g., New York Stock Exchange (NYSE)). In other, so-called over-the-counter (OTC) markets, participants operate directly via telecommunication systems. Market data are collected and distributed by markets them- selves and by financial data services such as Bloomberg and Reuters."

If the financial data is distributed by the markets themselves, can't a market change today's data by adding 1$ to each transaction so that the next day, transactions will start at a higher price than what it would normally be?