Hi again Keannu,
From what I have seen in U.S. English, it is standard to use a comma with coordinate adjectives (and to my knowledge, the same goes for British English, although if I am mistaken please correct me). In both of your examples, the comma would be used. I don't know if I'd say the rule is 100% absolute, but I think it is standard to follow the rule you have mentioned and I recommend doing so as good usage (in some cases the comma is indeed essential to avoid ambiguity, and in other instances is just standard usage).
Just to be clear, here is the idea:
Use a comma when the two adjectives could be reversed without a change in meaning and are separated by the word and.
No comma is used if one of the adjectives modifies the other. CMOS gives this example: "He has rejected traditional religious affiliations."
Here, saying "traditional and religious affiliations" would change the meaning. We also can't reverse the two adjectives because "traditional" actually modifies the compound term "religious affiliations."
Does that help?
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