No, think beyond how they are now. For a start it is a high risk event because it is a big event, mainly because of the sales, it could be sold gradually. Also more data would mean that valuation was easier.
Warren Buffett wrote a letter to potential sellers of business that he (meaning Berkshire Hathaway) was interested in buying. It should be easy to find as I think it is reprinted in one of Berkshire's annual reports.
The basic idea is this: it's easy to make mistakes in business. As a startup or business in general you made many mistakes over the years that you've had to learn from and bounce back from in order to build you business into the success it currently is. You've earned this competence through your mistakes, and these mistakes cost you at the time you made them. Most businesses only get sold once (acquisition or IPO), so you want to go to the people who know what they're doing when you go to sell your business. For all the shit investment bankers get, they are very good at their jobs.
Selling gradually doesn't do anything and makes the entire process far more complicated and time consuming, as well as potentially pissing off investors.
As for data, it isn't something that has been lacking. Moreover, IPOs aren't priced according to valuation (though sometimes bankers reverse engineer a valuation to satisfy a price).
