/How do you tell them all apart? Typical 3x3's, buttons and spikes can look very similar.
Learning to differentiate bucks by the slightest antler differences is a real art and takes a lot of practice. This is especially true when a property is loaded with 8-pointers. Quite often it's slight differences from side to side, differences between bucks on how much taller (if at all) the G2s are from the G3s, spacing between G2s and G3s, slight differences in the way points lean (forward, back, inwards, outwards) slight bends are "swoops" in tines or beams, how far apart the ends of the beam tips are, etc. And surprisingly, the best antler trait to look at is brow-tines. Brow-tines can be very unique. They can be tall, short, slightly mismatched, have a lean, or be farther out the beams from one buck to another.
Just finished up a census for one of my clients that included 99 unique bucks. The hard ones were the 17 different spike yearlings, and the 30 different 8-pointers.
As I'm going through pictures, each time I come upon a buck I've never seen before, I give him a unique identifier number and crop out pictures of him from as many different angles as possible, especially profile pics, and looking directly at and away from the camera. I then enter his ID number, number of points, and a brief text description of his rack into a spreadsheet. Each time I come upon a buck I don't think I've seen before I can sort the spreadsheet and look at the data for all the bucks I've previously identified with that number of points and see the text descriptions. Then if there are a couple that might be him, I can jump over to my cropped pictures of each of those bucks and see if he is already in the inventory.