I receive different, untainted coins (completely unrelated to the ones I earlier sent to X) from a different address Y to address B.
There exists NO chain of transaction between X and Y. Also not indirect, or coinjoined, or whatever. Nothing.
How are my coins in address B still blacklisted?
I did say 'taints ... to some extent'.
The anonymity set size of a single transaction is limited by the number of parties in it, obviously.
Unless chaumian blinding, zero knowledge proofs, or something dazzling has occurred, my statement is correct.