No it doesn't. It explains what the three as a group do; what I'm asking is, what's the difference between these three? Why did we need three separate commands? When (in the pre-SSH days) would you use one versus the others?

I'd assume rexec runs a command on a remote host non interactively; rsh runs an interactive shell on a remote host; and rlogin allows you to interact with login(1), again on a remote host. But I've not read the man pages as I'm on my phone.

Okay, but that's not the question I'm asking.

Each of these FreeBSD commands have man pages which your googling should have shown.

slogin is just a symlink to ssh, and sexec does not exist. So the s-commands' manpages tell me nothing about the difference between rsh, rlogin, and rexec, or why all three needed to be created.

rsh, rlogin and rexec each have their own man pages, which you should be able to find on freebsd.org if google is being difficult.

The irony here is that these manual pages are the very things being patched in the headlined message. Their exact locations in the source tree, and some of their contents, are right there in front of us.

So read the older man pages? Why is this a problem? You can also easily read the man pages for a specific version of FreeBSD here https://www.freebsd.org/cgi/man.cgi

Right. They say that rsh can be used to get a login or run a command on a remote host. So why do the other two commands exist? In what situations would a person have wanted to use rlogin or rexec instead of rsh?

Maybe rexec appeared first? And when rsh arrived later, they still kept rexec around? Perhaps they had a lot of shell scripts that contained "rexec" and didn't want to bother changing them to "rsh"? The actual reason is probably so mundane that maybe there is no accurate historical information on this topic.