lets say that i have a file stating a stock and the price which someone paid for it and the date. for example: apple (AAPL) 422$ 15/11/2011.
now apple have gone through many splits and possibly public offerings, or maybe increased their treasury stock numbers and any other activity which might affect the the number of stock available and the price of each stock. the problem that i have that historical data is adjusted for splits and all of the changes. and i wish to know the price that someone would pay with all the adjusting (something like 15$ in the apple example).
how can i convert that 422 dollars to the 15 dollars? i have many stocks, each one with different date and price. looking for a safe way to do those, and deviding by stock splits doesn't feel safe to me since stock splitting isn't the only option the change the price.
one idea i had is to use linear regression with x as the closing prices in the past (like 400) and y with the public adjusted data that i have (like 14.8) and use the result to convert 422 to 15. but i also can't find historical data with the 400 prices for 2011, all i find is adjusted. any idea how to convert?