Most of the 1860s SV's have square corners.The photographer's caption in the front was used mostly in the 1870's, while in the early 60s, photographer's placed their information using a pasted label on the back and later on a checklist of their views printed on the card stock.The thickness of the mount is also something to check.I'm not an expert, but I've handled a pretty good bunch of baseball views from the 60's and 70's.Here are some examples:Mid 60s (65-66)Late 60s (68-69)Early 70s (70-72)Mid 70s (76)I always try to buy SV's with good 3-D "focus"... It's always fun to recreate the effect using new technology. Think it worked with a great SV from Rob M. once.