A data point, obtained from a build of the time zone package as distributed:

Script started on 2024-12-08 22:23:57+00:00 [TERM="xterm-256color" TTY="/dev/tty1" COLUMNS="82" LINES="30"]
$ export TZ=America/New_York
$ ./date
Sun Dec  8 17:24:32 EST 2024
$ export TZ=Etc/Unknown
$ ./date
Sun Dec  8 22:24:55 UTC 2024
$ exit
exit

Script done on 2024-12-08 22:24:57+00:00 [COMMAND_EXIT_CODE="0"]

I could make an argument for: with TZ set to Etc/Unknown (or any other unfathomable value), some obnoxiously wrong results are best seen; a time zone abbreviation of ERR has been suggested as a possibility in the past.

Side note, brought to mind by /etc/tty and /dev/tty: if TZ is "-", should the time zone information be read from the standard input? :-)

    @dashdashado

On Sun, Dec 8, 2024 at 5:07 PM Brian Inglis via tz <tz@iana.org> wrote:
On 2024-12-08 14:41, Paul Eggert via tz wrote:
> On 2024-12-08 13:21, Guy Harris wrote:
>> (And, unfortunately, there's also no way to indicate "well, we*do* have a file
>> for that tzid, but it's not a valid file" - e.g., tzh_timecnt specifies more
>> transition times than are in the file - in a way that it can be distinguished
>> from "we don't have a file for that tzid.)
>
> Although POSIX provides no way to do that, tzcode does because tzalloc sets
> errno on failure and zdump uses strerror to tell the user. For example:
>
>    $ zdump No/Such/Zone
>    zdump: unknown timezone 'No/Such/Zone': No such file or directory
>    $ zdump zone.tab
>    zdump: unknown timezone 'zone.tab': Invalid argument
>    $ zdump .
>    zdump: unknown timezone '.': Is a directory
>
> (For extra credit, try 'zdump /etc/tty'. Maybe we should disallow that sort of
> thing....)

Disallowing these would also likely disallow variations on:

        $ zdump /usr/share/zoneinfo/.../...

        $ zdump <(...)

unless you just check the magic cookie?

--
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer     but when there is no more to cut
                                 -- Antoine de Saint-Exupéry