Yeah, so I made a mistake!
I caught it after I posted, and thought of posting a follow-up correction. Then I thought "no, I'll just leave it to see if anyone picks it up..."
This entry exists so I can point at the timestamp and say "yeah, I know"
"The number of Unix installations has grown to 10, with more expected." -- The Unix Programmer's Manual, 2nd Edition, June, 1972