I agree with this...sort of.
Does placing a few mushrooms in my FOWLR make it a Reef rather than a FOWLR? If so then I have 2 reefs. Does it count if I don't light the tank and the mushrooms eventually fade away and die? If not then I still have a FOWLR.
I see where you are coming from, but in my FOWLR the fish were the main focus and a few corals here and there were more of an afterthought rather than an attempt to keep corals in that tank. It was almost a place to ditch corals I didn't have room for in my reef such as mushrooms, cabbage leather, etc. The few that went in that tank didn't make it even though it sits in the window getting sunlight. (Well it did when we had sunlight anyway.

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The cool part about what you are saying is that we have come a long way in learning which corals we can keep in our previously FOWLR tanks with fish that will eat coral. So if I have a bunch of large coral eating angel's I simply don't keep corals they like to eat and instead keep corals they tend to leave alone. We have learned a lot about how to keep these critters together over the last 10 - 20 years.