evap lines always

Does an evap line show up every time after a test dries up when it's negative? The reason I'm asking is because I have a few old tests and they haven't really shown any change. if they don't have evap does that mean they could have been very very faint positive? I know the whole shpeal about not looking at tests after the time frame. I just wanna know if evap lines are ALWAYS there when negative

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