A lot of flavour is 'tasted' by smelling the food which you can't do when your nose is blocked.

And many people with smell disorders have problems with their sense of taste - e.g., see - https://www.nidcd.nih.gov/health/smell-disorders

On the other hand, you do still retain a lot of taste ability even with a plugged nose.

Try taste testing a firm raw potato or onion vs. an apple with a plugged nose. 
Our testers had no trouble telling the difference.

Also there will be differences between and within populations - there are hundreds of human olfactory receptors (exhibiting a range of polymorphisms) and hundreds of volatile chemicals found in food. Ajna, in your type of experiment do you obtain the same result(s) when you take into account shape and texture - e.g., if the products are emulsified?