You say that an extension of stay will not "officially" be cancelled if leaving, obviously without a re entry permit. Yet, the same extension cannot be used when re entering Thailand. We hear many examples of those who unknowingly leave Thailand without a re entry permit and have to come back on a visa exempt and start the whole NonB/NonO/NonEd process again. We are told that computer systems are linked now between border/airport entries and immigration. How would it work that an extension is not "officially" cancelled but in reality it has been as can't be used again. I am not doubting what you say. I'm just intrigued as to the process.
Just to make things clear....the type of visa that you used to enter Thailand with is irrelevant. A sixty day extension based on marriage, with the documents listed above, can be issued on any kind of entry. Usually a copy of the Tabian Baan ( blue book) will be required too.