|With Listserv 1.8c on an IBM VM/CMS  system, how can subscribers to a list be
|prevented  from ever  selecting  the CONCEALED  subscrpition  option? On  one
|particular list, the owner (not me) does  not want anyone to have a concealed
|subscription  entry.

That's because how NOT to do something is NOT documented ;-)

LISTSERV(R) offers no native mode operation to inhibit personal settings.
The only thing you could do is to manually or automatically issue

QUIET SET listname NOCONCEAL FOR *@*

at some CPU expense.  Of course this doesn't inhibit folks from subscribing
with phoney names or even * * or anonymous.