So, for example, you can literally get your own coins back when you make a withdrawal from a casino or exchange.
Or you can get entirely different coins, therefore have them mixed. I am pretty sure that a casino (apart from wagering requirements) works perfectly fine as a type of mixing service. I haven't checked every single transaction from the past, but as much as I can remember I never received the same coins back.
Even if you receive the same coins back, usually you can specify a new withdrawal address. How can anyone now be sure that the same coins hit a wallet of the same user? That data set can only be analyzed more or less conclusively if interested parties (investigators) have access to the account data at the gambling site. I think this boils down to small accounts mostly being ignored as the effort required by investigators may not be in line with the results they are hoping for. Not to forget that we are still talking about no KYC accounts, which means even if the relationship between two addresses could be established with increased effort in hindsight, it would still be a non-identified holder.
