Ian Jelf wrote

You get this on the ECML too, with slow trains from Cambridge being
advertised as going to Finsbury Park and so on.

It also happens on the Central Line, with trains leaving Woodford for

Central London via Hainault being advertise as for "Hainault", until
they get to Roding Valley, when they suddenly become destined for
Ealing
Broadway (or wherever).

It is a bit weird, but i think it's a good idea.

As good as any, yes. There's no ideal solution in these situations
and
each one will have pros and cons.

And if "it's lying" is really a common reaction, then change to
"Hainault & beyond" "Finsbury Park & beyond" and so forth which are
"true" but avoid providing a final but confusing destination.

"& route xy" is also possible.

I have previously noted that SWT has loops with both directions going
to Waterloo and, eg, Weybridge to Waterloo via Staines which are both
"long" rather than "slow" and use the same solution as above.

--
Mike D