UC Mandatory Reconsideration - Can payments be backdated?

We've just received a positive decision after 9 months waiting for the Mandatory Reconsideration (Universal Credit).

My partner has originally failed the Habitual test, meaning I was the only one on the UC account and our payments were lower.

They've now changed their decision and increased the payments from now on.
However there's no mention of any payments being backdated.

I saw this on the CitizensAdvice website:

What happens when the decision has been reconsidered

When the decision has been looked at again it will either remain the same or be changed by revision. Revision means that if the decision is changed, you will get any backdated benefit you're owed to the date of the original decision.

This was totally their mistake and my partner should have been on the account right from the beginning (9 months ago). Are we allowed for any payments to be backdated? If so, is there anything we need to do to claim those?

Thanks in advance!