Comment by Spivak
This article isn't for you then, this article is for people who have casually heard that exactly once delivery is impossible and take it to mean exactly once processing is impossible. When someone talks about at-least-once and at-most-once in the context of well-known queueing systems they say will say delivery but will mean processing, because as you say, they're the same in practice.
You typically hide the processing bit so that from the perspective of your application code it really is exactly-once.
> this article is for people who have casually heard that exactly once delivery is impossible and take it to mean exactly once processing is impossible
Those people would be better served by approximately two sentences clarifying that exactly-once processing is a different thing that can be achieved with at-least-once delivery and idempotency, rather than 20+ rambling paragraphs of redefining formal terms.