what happens to historical prices after a rights issue

Are they adjusted to the market cap at that time divided by the current number of shares outstanding (after rights issue)? This essentially accounts for the dilutive effect, correct?

I think this is the adjustment used in Google’s market summary charts. This essentially gives the value of your shares if you do nothing at the rights issue and let it dilute your shares. However, the data published by the Financial Times are wildly different. For example, the price of IAG on 31 Jan (way before the rights issue) is shown to be 229p by Google. So if you purchased at that time it would have been around 572p per share (the rights issue was 3-for-2). If you then fully exercised your rights to the new shares at 92p per share, then your average cost would have been 284p per share. However, the Fianancial Times shows that price on 31 Jan to be 377p. How on earth is this calculated?