I recently visited Vietnam and had a good time. I had a full page one time use only visa. I'm pretty sure I will be going back to visit again in the future using the same passport.

Obviously I would need a new visa for the next trip. When you apply for a new visa do they cover up the old one, or do you start a nice collection of full page visas?

I don't want to get into the details of multi-entry visas and whatnot. Let's assume I would be visiting infrequently and not able to utilize a multi-entry visa.

So basically, does your passport start filling up with a bunch of one page visas? Or can they change your old one, or put the new one over the old one? Do different countries do it differently?
Thanks