I had a sneaking suspicion something like this may be the case, I'm glad I asked the experts as it wasn't very clear to me (the whole same-day change seems to be a bit underdocumented).
Originally Posted by
corporate-wage-slave
I have to say, it really is best to avoid adding a POUG unless you are 100% sure of taking the planned flight.
And that is probably the best advice which I will follow. Thanks both.