Can’t login to wordpress despite changing password to something known directly in MySQL or using “Password Reset by Email” feature

WordPress does NOT use the MD5 hash for passwords anymore. It uses the PHPass library to generate secure password hashes.

However, WordPress will support MD5 hashed passwords. On the first login of a user with such a password, it will detect that case and change the password entry to be the newer, more secure, PHPass version of the password.

Therefore, the codex is not wrong. Putting an MD5 password into the DB will work and let you login, due to this backwards compatibility.

That said, the password reset by email, if you get the password, can’t be mistaken. Perhaps something is wrong with your database itself or you’re having caching issues. Try repairing the database tables using phpMyAdmin or similar.