It can happen that occasionally you get stamped incorrectly (e.g. additional months, years etc.) - if that's the case it is your responsibility to go back to immigration and make them aware of it and have them fix it

Sorry for the off topic, but I'm reading a lot about Non O visas and 90 day border runs. I'm a Non-O holder (not retirement), based upon my Children / Family (not marriage) and I also have an insurance + WP + TM30. All I normally do is to get my yearly extension at Chaeng Whattana and make my 90 day Report there. Is the border run a new thing?

Seniors, families with infants and others in e.g.wheelchair / invalid get the "priority lane " (it was my case when we traveled with our 1 year old)

Why not

I already have dual citizenship - I won't need another :D Technically I am perfectly fine with Non-O and don't see any real benefit in going "further"

Shouldn't you get another 30 days when returning / on arrival in BKK from Mandalay?