Congratulations on that excellent (and unexpected!) result. It can be enough of a challenge to rear a full brood to independance when both parents are feeding, that is a great hen to have gone on to lay, incubate and rear such a long time after the cock was lost. While extended sperm storage has been recorded in parrotlike and poultry I agree that fertility in the latest eggs is very unlikely. It would certainly be worth putting on record.
My own pair of shamas have now commenced moulting and will have to be separated as the hen is becoming aggressive towards the cock.
I have two more white-eared bulbuls close to fledging, these will be the final youngsters for 2018.