I had the opportunity to pick up a couple more GSM bars recently. These bars have a nice clean design, which I like. I don't have any way of knowing how old these are, because this design is still produced today. You can pick them up at the Golden State Mint website. The company itself is located in Florida, and according to their website has been in operation since 1974.
But on to these specific bars. As I said, I have no idea how old these are, but they certainly appear to have been around a while. There is some toning on the bottom of one, and scratches and nicks are present throughout. They've got a lot of carbon scoring here; looks like these boys have seen some action.
The other thing I found interesting is that they appear to have different finishes. The one on the right has a mirrored finish (you can see the reflection of my phone across the middle), and the one on the left has more of a matte, or maybe frosted finish. Not sure if that means these were produced at different times or for different purposes, but the difference is noticeable enough that I would call it a variation.