FAQ for
A Matter of Life and Death (1946) More at IMDbPro »

The message at the beginning says:

This is the story of two worlds, the one we know and another which exists only in the mind of a young airman whose life and imagination have been violently shaped by war.

Which then scrolls up to reveal:

Any resemblance to any other world, known or unknown, is purely coincidental.

That is the get-out clause. They're leaving it up to you.

In 1946? No, the effects in this film were all done the hard way. But they are done so cleverly that it's sometimes hard to tell.