In my recent "Ultimate RoW" run, the reason why I ended up with so many excess +12 equipment was because I want to get grim on bow. After maybe 100+ stones later and I ended up settling with vampiric.
What I observed was the enchant keep looping around several enchantment and not totally "random", not really in fixed order so I guess that is the random element. So if grim are not in that particular loop then I will never be able to get grim from stone enchant.
Is this observation true? If yes, then how I change or break out to another different loop?
Some random item drops do use a 'deck' system to try and improve consistency, but that's only for stuff that spawns at part of level generation. Enchantments should be completely random each time, but it's very easy for our brains to percieve patterns in random results.