So I went looking, and after some searching, I finally found the Mulvaneys at 270 Van Brunt St., and I was slightly surprised by the results, given what I thought I knew. Julia (age 57), Willie (age 28), and Harold (age 24) are living together at 270 Van Brunt. She's widowed, they're single, none has gone to school in the past year. No surprises there. However, Willie is now listed as being able to read and write - AND, he apparently holds down a job, as a Bookkeeper for an insurance agency! That's not exactly what I expected to find, given that last we checked, the 20-year old Willie was illiterate, he didn't speak until he was 10 years or older, and when he died just 3 years and 10 days later, he was listed as having no job. (I believe you were supposed to list "usual occupation," even if the individual was not working when he died - however, we do know that Julia just listed "Retired" for Patrick, so she may not have been in the practice of filling out death certificates to include former occupations.)
Perhaps I've been overestimating the severity of Willie's condition? This is entirely possible, as I know next to nothing about Willie's condition. Another unlikely possibility is that whoever answered the door - Julia, Harold, or Willie himself - could have lied to the census taker, to make him seem like a more productive member of society. In further speculation, it's possible he was some kind of savant, having limited communication but amazing math skills.
In other words, I'm now writing fiction, which is not the stated purpose of this blog.
Other interesting pieces of information we pick up from this census are that Julia's rent was $18 a month (what happened to rents like that?!), that neither of the boys had been in the military, and that Harold was a "Checker" in the "freight" industry - that seems relatively consistent with a job on the docks, I think, though I don't know what a "checker" is, unless it's exactly what it sounds like, and he checked things for a living.