I think we’re all in agreement that these keys should accept multiple values. My point is that, for some keys, the number of values also says something about the feature (such as the number of flags on the pole). Adding empty or duplicate values to align with a different key could mislead a data consumer. So even if the answer to question (3) in your original post is that the architect=* and architect:wikidata=* tags are correct, I don’t think your example works as a general rule for every *:wikidata=* key.