What behind-the-scenes checks happen when passing through passport control at an airport?

This will depend on the countries involved, and potentially the airport. There certanly are international databases of lost and stolen travel documents, e.g. the one run by Interpol, however in general countries don't directly communicate their lists to each other and certainly don't allow all countries direct access to their own passport databases. In many cases the port of entry will be checking a local mirror of international database, or even a reduced list of unexpired stolen passports.

All this means there can be considerable delay between you reporting your documents stolen to the issuing country and an official in another country (or indeed the airline you are travelling with) having the opportunity to identify it as stolen, assuming their infrastructure is set up to check.

In my experience, the level of checks is highly variable:

• at many land borders, where there is often a lot of cross-border traffic, it is not unusual for officers to wave through the vast majority of people, or even for border posts to be closed at times. They often will only stop people with plates that identify them as not from the local area, for instance. If they stop you, they may just go a quick run through the passport to check for obvious signs of forgery, but while they are standing there next to your car they just don’t have access to any database, so the only way for them to check is to go back inside and so on, which will delay everyone else.

  In countries where they are not allowed to strike, that’s actually a way for them to put pressure: in France we call it “grève du zèle”, it means they will suddenly start checking a lot more, which will slow down the flow through the border, cause queues and delay, and will soon be escalated.

• in many places, the queue for “locals” will see anyone with an ID in hand either waved through, or the ID given a cursory check. It may vary quite a bit, but French passport control officers for instance do it a lot.

• in other places they do more checks, though they often just check their national databases for people who are wanted, who are not welcome, or check for the existence of a matching electronic visa (ETA, ESTA, eVisitor, whatever they call it).

There are indeed international databases of stolen passports, but:

• the country who produced the passport must cooperate and send the data to that database. It may be a long process, often done in batches with large intervals. There may be a large number of intermediate processes and databases in the middle.

• the country you are visiting must use that database. And it needs to have a way for officers to check it. Obviously in some countries just scanning the passport will automatically do all checks, while in other it will just check the local database and a separate query must be done to check the global database. There may be delays in updates all along the way. Some places may have poor connectivity so they would only have a small local database rather than direct online access to the full thing.

In many locales, passport control operations are severely underfunded. You can see officers using PCs that seem to go back a decade or more. Systems are often very slow to change.

There is very little incentive for many countries to put a lot of effort into that. They all talk about security and controls, but when it’s time to pay...