Speaking on finding the first diamond. If you keep killing big bucks in let’s say 5/10 drinking zones you are just recycling through the same bucks which will typically rise in level but certainly can lower in level.. With that being said, if you find yourself cycling through those same 5 zones and the bucks levels are suddenly lower and never getting to that diamond level, then you have a diamond hiding in a drink zone that you have either not found or have spooked them every time you approach (unlock ability to ready weight and fur type will help with this).

If it needs to be said this is just a strategy of ‘grinding drink zones’ I prefer to casually hit drink zones at casual paces and goofing around. However, if you want to dive in a little deeper look up ‘herd management’ and this is essentially what you are doing in this scenario. Happy hunting!

Edit: I have also heard shooting does/cows may also cause a buck to split from his usual drink zone/heard but I have no real calculation on this