You agree not to license, sell, lend, or transfer your account, Discord username, vanity URL, or other unique identifier without our prior written approval. We also reserve the right to delete, change, or reclaim your username, URL, or other identifier.

If transfer of accounts is a policy violation, then Discord has legal cover to confidently assert that, once ID is verified, the ID'd person is the owner and controller of the account thereafter.

Account selling, stealing, and sharing will certainly still happen, but that's grounds for banning, and not Discord's legal liability anymore.

Then why could they not also legally get away with using account age as a proxy?