(a) Ordinarily, a written request that the benefits of a miner or surviving spouse be augmented on account of a qualified dependent is made as part of the claim for benefits. However, it may also be made thereafter.

(b) In the latter case, beginning with the month in which such a request is filed on account of a particular dependent and in which such dependent qualifies for augmentation purposes under this part, the augmented benefits attributable to other qualified dependents (with respect to the same miner or surviving spouse), if any, are adjusted downward, if necessary, so that the permissible amount of augmented benefits (the maximum amount for the number of dependents involved) will not be exceeded.

(c) Where, based on the entitlement to benefits of a miner or surviving spouse, a dependent would have qualified for augmentation purposes for a prior month of such miner's or surviving spouse's entitlement had such request been filed in such prior month, such request is effective for such prior month. For any month before the month of filing such request, however, otherwise correct benefits previously certified by the Office may not be changed. Rather the amount of the augmented benefit attributable to the dependent filing such request in the later month is reduced for each month of the retroactive period to the extent that may be necessary. This means that for each month of the retroactive period, the amount payable to the dependent filing the later augmentation request is the difference, if any, between: