I just checked the US Amazon site and found
The Quatermass Xperiment on sale at a low price in a US edition. The cover says
The Quatermass Xperiment in large print followed by
.....The Creeping Unknown.
Those lurid titles from the 50s and 60s were so commonplace for American horror films (flicks

) that they became a joke even at the time, and now they are usually a clue that a film is second or third rate. Occasionally they go back to the original title. The Qatermass films are known by that name here among those who like them.
Also, I found that to be the the case with the excellent
Night of the Demon. It was shown here on TCM early in 2007, and the original title was used. Also, there was a note at the beginning saying that some footage deleted for the US release had been restored.
Our fears in Banquo
Stick deep; and in his royalty of nature
Reigns that which would be fear'd: 'tis much he dares;
And, to that dauntless temper of his mind,
He hath a wisdom that doth guide his valour
To act in safety