I've seen these words used in the following sentences:
Judging from these examples alone, I guess they have some kind of overlap.
When is it appropriate to use one over the other?
I tend to think of 以後 as meaning one or more specific points after whereas 以降 means most of/the whole time after. But I'm not positive that they don't overlap at all.
one or more specific points after
most of/the whole time after
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11 months ago