It's really unfortunate that some Annona sp. are called "Custard apple" here, even Cherimoya and Sugarapple are called Custard apples. Not many people know the name Atemoya or Cherimoya for example.
I don't use the name Custard apple as it is very vauge and downgrades the fruit by comparing it to some strange human concoction. Annona sp. is more botanically correct in my opinion, the best is obvoisly to state them independently with latin name.
For example the A. diversifolia looks very similar to a A. squamosa, is it a Custard apple? YES, according to the definition but noone here calls them Custard apple's.
It is for sure an Annona sp. so I deduct that the logic for using Custard apple is flaud and bound to create confusion. Until better definition is given.
The meaning of CUSTARD APPLE is any of several chiefly tropical American soft-fleshed edible fruits.There are also other soft-fleshed edible fruit that are definitly not in the Annonace family, If I called tomato a Custard apple people would be very confused indeed. But it would be correct by the definition.
https://www.merriam-webster.com/dictionary/custard%20apple