Is there a minimum passport validity requirement when applying for a non-O marriage visa extension in Thailand?

@Scott ********

Many MANY years ago, if your passport was expiring before the extension ran out it didn't matter, they'd just give you the year in the old one,

THEN

They changed to giving you an extension until the passport expired but when you brought them the new passport they'd "give" the rest of the year you were shorted by the other passport running out

NOW

you get an extension valid until your passport runs out and you lose any time you were shorted.

@Scott ********

loose the year on the passport much better than having to re do the visa again.

@Scott ********

, Unnecessary additional information.

When you get your new passport, your old passport is invalidated. Your extension and related stamps on the old one are transferred to the new one. Those stamps have the same dates as those stamps in the old passport, it looks like several months of "rest of extension" are transferred to the new passport after the old passport is invalidated. It doesn't mean you had an extension longer than your last passport validity or any extra period was added.

You may be able to check your stamp on one of the early pages of your passport and the expiry date of your old passport.