Words and the way they are put together are not science. I would guess that 99% of spoken utterances are made without planning, and many, many things are written without real thought. Grammarians and lexicographers simply try to see some form of order in what native speakers produce.
I would suggest that you try to take a slightly more relaxed approach to the language. General rules are (generally) helpful. It's not the end of the world if not everything can be neatly slotted into a precise position in some artificial grid.
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