Ed, The thing that still remains most perplexing is the Many Directory Listings with Ruby and William (WJ) Diers living at 316 Mesa Ave !
Can find no explanation how the 2 unrelated families of the same name being at the same address---- except happenstance. Or, they are related and I haven't found the connection.
Today, that residence is a triplex. So I agree with your theory that the census taker might have been confused by all the people inhabiting the residence .... Which are now 3 apts of about 1200 sf. Or, only got the one family and forgot to return to get the other (s) ????
No Ruby with WJ and Roger in 1940
No Elizabeth with WJ in 1930 in KY or elsewhere
Searched and searched with every wild card and misspelling, and not finding them. Hiding, missed or what?????