The only information I have is about Germany but in other theatres the RAO staff will know if an LOA Review has been carried out and when its results take effect.
Generally, whenver the FFR changes in any currency, LOA is adjusted too. Somewhere there is a magic equation whereby the number of Euros/Dollars or whatever local currency you are paid in remains constant for those who have the majority of their salary paid overseas and leave a fixed sum in UK to pay ongoing commitments there, eg mortgages, insurance, loan payments..... This is what is happening to us in December - FFR falls, LOA rises to make me no worse off at the end of Dec than I was at the end of Nov.
Where this falls down is for those people who "reverse" the situation and leave most of their salaryin UK and send a fixed amount of pounds overseas - whenever the FFR falls they will see less money arriving in the overseas bank and may need to adjust their split on JPA.