That writer is pretty good to be able to tell the same deer year after year without any markings or tags
he probably has 100X the exposure to live deer than most on here, and LOTS of exposure to that herd. It ain't that hard to id individual deer IF you see em a lot AND pay attention. Every dang one of em has some characteristic that stands out, be it looks or actions.
I have a buck on my place I call Squint, he always has his head up and looks to be squinting. EASY to spot.
I worked on a place that had a buck I called Junior, I saw him for several years, several times every week. I spotted him from across a 250 yard field on day after he had dropped his antlers. I told my wife it was Junior. She told me I was full of it if I thought I could id that deer from 200+ yards without antlers. I told her he had a scar on his other side and described it for her. When we drove closer, 40 yards, he turned and there was the scar. HA!!! Like I said, not so hard IF.....