And that reasoning of writing the form to just be postcode and flat number is why I can't get my address into forms.
There are two flat 1s in my postcode.
One place that would not work was the local council and so I could not get anything done, it took over a year of phoning up for this to be fixed. (of course the council tax database got it correct)
I wish companies would fix their addressing. My address has the form:
1 Example Close
Somewhere Drive
But often when entering your postcode and selecting a house number, the address ends up as "1 Somewhere Drive" - which is a different place. The forms don't seem to realise that some locations should have multiple address lines. Fortunately in the UK, the postcode helps ensure our mail (mostly) arrives.