Agreed that adding all the addresses in Casterton is a great goal, and should help with deliveries. Please note that the data in the Royal Mail address database is not licensed for use in OpenStreetMap, so you unfortunately cannot (and must not) use it to fill OSM in.

There’s some information about this on https://wiki.openstreetmap.org/wiki/Postal_codes_in_the_United_Kingdom

The best information which we _can_ use is the postcode centroids data, which is available in the ‘Postcode centroids’ layer in ID. It’s what Royal Mail have chosen to release freely. For cul-de-sacs and short residential roads, it’s fairly easy to associate the centroid with the street. For longer streets, or where the postcodes differ for odd/even numbers, it’s a bit harder.

You might find that if you use the format you specified, but omit addr:street (for the houses with no associated street name), then StreetComplete will start to ask you about the street names for the houses again. That’s where my confusion before arose. StreetComplete expects either addr:street and addr:city to be set, or no addr:street and addr:place instead.

This (and the fact that post towns are outdated) is why I suggest going with a combination of the first and third tagging schemes I listed (the first for addresses which have a street, the third for the others).

You could try your tagging scheme and see if StreetComplete starts to ask about street names again, though, if you wanted.

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I (and other editors who’ve been around a while) check all the edits in the north west of England. Mostly it’s to prevent vandalism, but also helps with catching tagging mistakes or typos while the edit is still fresh. With relatively new users (such as yourself) it also means we get a chance to provide some guidance on some of the trickier aspects of editing OSM, like this! :)