Arrears of CA- when do they count as Income?

Cl has had an overpayment of UC due to CA being paid after UC had already paid for the month.

It seems safe to assume that the payment must have been received in the assessment period after the one in question so are there any rules that allow UC to treat income as being received on the day it was due to be paid rather than the day it was actually paid (like the rules for occupational pensions etc)  and shouldn’t any arrears of CA be counted as capital anyway?

Sorry if this is obvious but the more I look at it the more confused I make myself

CA is unearned income, and doesn’t depend on when it is actually paid.

There will have been a change of circumstances on the date CA entitlement began. Under the regular supersession rules, that change has effect from the start of that AP.

The amount normally taken into account each AP will be the monthly equivalent (i.e., the weekly amount multiplied by 52 and divided by 12 - see Reg 73(2) of the UC Regs). The actual dates CA is paid is irrelevant.

However, in the first AP, the amount will be reduced as per Reg 73(2A). (If not for this provision, the full monthly amount would be included in the first AP, even if entitlement only began on the last day of the AP.)

As an aside:
On basic principles, for the AP during which entitlement to unearned income ends, no unearned income at all should be included.
However, the inclusion of the words “or ends” in Reg 73(2A) makes it clear that unearned income should be included in that last AP, and presumably overrides the normal supersession rules. But the drafting is horrible!