From The Alfred Hitchcock Wiki
Windowboxing is a method of compensating for the overscan which exists on many television sets -- especially in cathode ray tube (CRT) sets. When viewed on a television that does not have overscan, windowboxing appears as a black border around the image.
The majority of Hitchcock DVDs do not use windowboxing and only a few make use of it for the opening title sequences.
The only Hitchcock DVD that uses windowboxing for the entire transfer is the 2007 Criterion re-release of "The Lady Vanishes".
The original release from Criterion did not use windowboxing...
...whereas the re-release does...