Avanti West Coast will not tell you whether you've passed to National. They require Enhanced (and it is a high standard indeed) and if you fail one but pass two of the computer tests, they will simply tell you that you failed, and walk you out of the building. OPC are about as useful as a chocolate fireguard in enquiries as well, afterwards.
OP mentions that he has sat for TFW twice. TFW require only National. A former colleague of mine who sat for Avanti and got as far as the computer tests (passed the hand eye, passed the traffic photos, failed the black square) had to resit all three parts of the computer test (hand eye, photos, black squares) for TFW but crucially, did not have to resit the paper tests or pre-assessment tests.
The issue is, is that the computer tests are all done on one console, in one sitting, consecutively with no official breaks betwene tests or distinctions such; this is one element that makes them harder than they seem.
to answer OPs query, if you failed even one part of this section twice, ie failed the section overall, twice, than it is game over and you cannot try again for a Driver until/if when OPC changes the tests, I'm sorry to say. It's a bleak and horrible moment for any so-called 'railwayman' who sees the railway as more than 'just a job' but it is a heart wrenching reality alas.
I wish you all the best in finding happier pastures elsewhere.