Recognition of Loss Allowance

Dear Teacher,

Regarding below notes in ACCA Study Hub :

“Credit losses are recognised immediately in profit or loss with a corresponding credit entry to:
An allowance account in the case of financial assets at amortised cost. The allowance account is offset against the carrying amount of the asset in the statement of financial position.
An accumulated impairment account in OCI in the case of financial assets at FVTOCI. The carrying amount of the asset remains at fair value in the statement of financial position.”

They provided an example of a debt instrument (FVTOCI) with the fair value of the asset has fallen from $2,000 to $1,920; $60 of the $80 fall in value is due to 12-month expected credit losses on the asset and the remaining $20 fall is related to movements in the market value of this type of asset. Below is the entries:

Dr Change in value of FVTOCI financial asset $20
Cr Financial asset $20

Dr Impairment loss (profit or loss) $60
Cr Accumulated impairment account (OCI) $60

I do not understand why the fall of $60 did not go to the ” allowance for impairment account ” but instead an account called “Accumulated impairment account (OCI)”
1) what is the difference between the two accounts?
2) Why it is a credit in OCI ? it gave me the false illusion of a “Gain”….
3)Will the balance in OCI brought to the FS of future Financial years?
4) In this case, will the interest revenue being calculated based on the Fair value after considering movement of market ( from $2000 -$20= $1,980)? I understand that with 12 month ECL the interest revenue is based on the full asset amount , no consideration of the loss allowance account but what is there is a movement on FV.

Thanks,