Thanks guys,

I am still puzzled by this. Really not the first time I have an itin change after check-in, and that never happened. Maybe next time I'll just tell the res agent to 'clean' the file after the change, whatever that means! Thanks anyways!

PS. With regards to claiming back my original seat, it did not even occur to me as there was this long queue of pax behind me waiting to board, but as soon as I saw my seat, I regretted it... But in the end I did survive and got to my destination safely, as per my contract with AC!