Yes, obviously, maizie, we have all learned to read, so probably learned more by doing, rather than learning 421 correspondence as theory before being unleashed on the printed word.
There are very few words in English that have a unique spelling and because they are so unusual, they are easy enough to learn. But there thousands of words (possibly most words) that could have more than one phonically legitimate spelling and we have to get to know which actual spelling is correct. Your suggestions of grouping words by correspondences or having a 'spelling pronounciation' are useful ones - but there is still a lot to learn, whether by conscious effort or just by experience.
^"what you can't be expected to know is that that there is definitely no such word as 'blow' which rhymes with cow."
In which case, as we're always being told that these 6y olds expect words to have 'meaning', it's most likely they'd go for one which they 'know'.^
Id assume that children would be most likely to go for the one they know, but it tends to be critics of the test that tell us "that these 6y olds expect words to have 'meaning'", rather than defenders of the test. If the test is diagnostic, what does the test tell us about children who mis-read the real words in a phonically plausible way?