I think I get your question now. A Pokemon evading an attack has nothing to do with evasion boosts, or even to do with the pokemon being attacked. It is only to do with the move used, which, if it fails, has a pre-arranged way of failing: missing, or being evaded. At some point in the move being made, in the game's programming, it can either hit or miss. If it hits, everything is fine, but if it misses, either message can come up, depending on the move. They are essentially interchangable. On the chance that the defender did have evasion boosts, it would be more likely to 'miss', which would result, depending on the move used, as either being evaded or missing, but would not influence whether it would be one or the other.
I may have just missed the point again, but that sounds like what you were asking.