Thanks.
Since the Apple ID is old and hasn't been used since 2012, Apple doesn't recognize it as someone's current Apple ID. I get an error message saying this when I go to the link you kindly provided.
Please keep in mind that this email address is no longer even functional. The domain provider has gone out of business, Thus, I cannot use even a "Forgot Password" form since there is no email address any more to send the password reset link to any more.
My problem is that I bought things while this email was my apple ID and now, every time I reset any of my Apple devices, they ask for the password for this old apple ID (so that I can still use the things I bought using it a long time ago). But, I no longer know this old password.
How can I get my devices to let me use and sync the things I bought with an old apple id whose password is now unknown?