You can look at the links and while you cannot really see the peened ones, you can see that the older style (8-speed and lower) chains are not peened. They have pin extending past the outer link and it is not hard to tell that they are just cut square. That peened pins have a slight "mushroom" to the pin end. That mushroom is right at the outer link plate so it is hard to see.

If you are looking at a link that has a pin that obviously could be driven in a little more or less and it wouldn't be an issue except for bugging OCD types, you are looking at a pin you can drive out and reuse. (That chain will also not work on a 9-speed or higher cassette and will ride up on the teeth.) I happily drive 1/8" links on my fix gear at will to lengthen or shorten chain. I try not to do the same link twice, but it happens and has never been an issue. (I've been riding those 1/8" chains and before that, old 5-speed chains on my fix gears for 100,000 miles. Plenty of time to test my theory. I also have two bikes set up 7-speed. I use quick-links or re-use the pins as I see fit. My 9-speed always gets a quick-link and I see to it I always have a new, boxed chain in case anything happens. (They don't always run well if the cogs are worn, but at least they are safe.)

Ben