Donkey - identity theft works by selling the details of a batch of inidividuals to a 3rd party - maybe 1000 people at a time. The 3rd party can go through that list of 1,000 ID details, and attempt to use their identity for fraud. Sure, plenty of those attempts will fail, but at least a few out of those 1,000 will work. If I saw in a list of 1 million people a subset of people who had been flying frequently, I would target them as more likely to be wealthy and better candidates for fraud.
ID theft doesn't necessarily work by targetting specifically Mr John Smith of 32 Cherry Tree Lane - it's done by systematically going through a list of essentially (but promising) random IDs and just picking off the ones that work. The details that don't work can be simply discarded while the ones that do work can be milked for benefits
Amending relatively minor details like date of birth - perhaps out by a year being put down as a typo - in online checkin mean a busy gate agent probably won't even bother performing a rigorous check (boarding card may show only name and passport number, and as an EU passport is almost always good for entry to any EU country there is no need to worry about immigration fines) - but it's enough to mean that any attempt of using my details fails in any form of fraud through impersonation.
Anyway, this is digressing - can anyone provide info on what validation checks are performed in the process of providing passport details by the airline to the Govt of the arrival country ?