What did that project really pay?
The quoted rate is the number you remember. The effective rate is the number you were paid.
Result
That money was recoverable.
Not by arguing after the fact, but by pricing each request at the moment it was made. Start with whether your contract even allows it.
How the two numbers differ
Work you were not paid for values the extra hours at your own rate. It is what that time was worth if you had sold it to someone else.
Margin values the same hours at what they cost you, worked out from the margin you expected on the quoted scope. Costing unpaid hours at your billing rate would make the damage look larger than it is, so this does not do that.
Margin is reported in percentage points. A fall from 30% to 10% is 20 points, which is also a two thirds decline. Both are true and they are not the same number, so only one of them is shown.