How do Immigration check your Visa status at the airport when you leave, if you have to get a new passport whilst in Thailand?

By using their computer.

With your fingerprint and eye scan !!!

Did you forget about that when you flew in ?

You go to a immigration office with the police report for your lost passport and they will reinstate your arrival stamp based upon their records.

Your name and date of birth don't change just because you lose your passport. That alone is enough to locate your immigration record.

 

To confirm your record the database contains your photograph from when you entered the Kingdom, and also your fingerprints.

1 hour ago, ubonjoe said:

You go to a immigration office with the police report for your lost passport and they will reinstate your arrival stamp based upon their records.

I actually tried that about 7 years ago after my passport had been stolen.  I took police report, new passport and details of my last entry (flight/date) to Jomtien immigration but they had no interest at all.  I was on a 90 day non-O entry.  Simply said I wasn't on their system and told me to go to the airport.  Which is what I did a week or 2 later, no problems at all, IO wrote a story on the first page of my new passport but as the old visa was lost I just hopped to Singapore and back in on an exempt entry.  Thereafter a few weeks later I think I went to Penang (possibly Cardiff, very similar places) for a new non-O.

11 hours ago, Raphus said:

With your fingerprint and eye scan !!!

Did you forget about that when you flew in ?

Since when do they do eye scans?