Saw a JD 700J LPG today near the office complex where I had an appointment so I checked it out. I was surprised it did not have a conventional drive sprocket but one that you could replace without removing the track it seemed. Each sprocket is made up of five parts that just bolt on to the drive wheel. It was a rental unit and hoses and blade had been roughed up pretty bad but the rest looked OK.
It stated the track that was supported on each end and in the middle with one roller should have a 2" +/-1/4" sag in the track. Expect the Komutsu in the photo has been worked on by a none skilled owner, etc. It could be someone is just trying to conceal track wear I guess perhaps.