I'm not addressing the main thrust of your question, but this particular item about an error caught my eye. I had similar issues about entries for my parents in city directories. After discussing it with them, I came to realize that often (but not always) the entries in city directories are a year in arrears. That is, the data might be collected in 1929 and published in the 1930 city directory. And the collection process might take place at different times during a year.
Also, I discovered that at least some city directory companies had two sources of data. One was a house to house canvas. The other was employment roles from local employers. So the "sometimes a year in arrears" data problem can hit either source of data and sometimes both. Also, the exact name listed from the house to house canvas can differ from the name provided via employer rolls, so there can sometimes be duplication and/or inconsistency in the city directory data.