On 23 Jan, 11:11, Steve Fitzgerald ] wrote:

All (Heathrow) trains do call at T123, just that
the T4 ones take about 10 minutes longer to get there.

(snip)

The T4 trains will actually display T4 & 123 as a destination; the T5
trains will show T123 & 5 as a destination.

So for people heading to T123 in a hurry, and the first train is to T4
& 123, perhaps the best strategy is to board it anyway and then lean
out of the carriage at Hatton Cross to see if the platform departure
indicator (assuming that there is one) shows a T123 & 5 train less
than (say) eight minutes behind.

PaulO