All 'fixed' bid contracts are done on the same basis regardless of scale. Low bids assume the specifications will change and changes are where profit is to be found.
When you have up to 20 billion dollars in the procurement pipeline at any time, cost of money and float are also large profit generators. Hell in the engineering phase document reproduction and handling are very often the largest profit center for the project. There is NO such animal as a "fixed cost" contract in EPC since each phase is commonly under different contract terms and conditions. Larry will find this out when he is torn apart in court assuming this ever sees the light of day.
Larry is going to find out that these projects are done by multiple project taskforces each with its own contract budget and infrastructure. This has absolutely NOTHING to do with AA accounting practices and everything to do with Larry's abysmal understanding of why he filed this suit in the first place.