I’m not sure what you are saying. Maybe this is what you are talking about: B’dieved (retroactively) if you said a shehakol on any food, it counts. But you are not allowed to say, “I don’t know the bracha, so I will just say a shehakol”. You have an obligation to find out the right bracha, and you are only allowed to just say shehakol out of doubt if it’s really impossible to find out (for example, the Poskim themselves aren’t sure and never reached a definite psak) or if you already said it by accident. Is that what you are talking about?
I certainly have never heard that there is any problem with making a bracha on 2 other foods that have the bracha that you are not sure about.
But if you think it might be better to know for sure what bracha to make on the blended vegetables, ask your Rabbi and while you are at it, ask him about this principle you are talking about.
You really shouldn’t be asking halacha questions to anonymous online posters. And the blended vegetables question is definitely one that should be asked because it may depend how well they are blended.