You’re right.
Can I use the new form or same old form?
Can I Include a copy of the old signed form too?
Is it possible to email it to AVO instead of mailing it?
You need to use the new form, the old one isn't tenable anymore, reason why it got updated.
You don't need to attach a copy of the old form, they have it in their records.
You don't need to send hard copy, you send a mail and can do webform upload too..
Send the form with a cover letter admitting it was an error of oversight.
There's no more document to be asked, if you beat them to it.
You don't want to have to be given an ultimatum to explain why you didn't disclose previous denial, when your case is being reviewed.
Please send it ASAP, AVO is being fast now, they might get to April applicants in no time